Colonel Jack O'Neill is brought out of retirement to lead a new expedition back to Abydos, only to find an old friend, a new enemy and a far wider use of the Stargate.

The team, now designated SG-1 are planning their next foray through the gate as they try to map out the variety of sites available to them and locate their missing friends. O'Neill asks that Teal'c be allowed to join his team but Gen. Hammond thinks that will be unlikely given that he is the host for a Goa'uld. Unknown to anyone, however, is that O'Neill's close friend, Maj. Charles Kawalsky, leader of SG-2, has been infected by a Goa'uld, an immature version that has not yet taken complete control of the host. Kawalsky is having regular blackouts during which the Goa'uld is trying to return to the gate. An MRI reveals what is wrong but it's unlikely the creature that has fused itself to Kawalsky's spine can be surgically removed. Meanwhile, Col. Kennedy arrives to question Teal'c who has pledged his loyalty to his new world.

The Stargate base is put in deadly peril when it is contaminated with a dangerous infection which causes its victims to become mindlessly animalistic brutes.

When Jack is injured unintentionally by a crystal alien, the alien duplicates Jack's form and out of fear of retribution tries to heal Jack. He returns to Earth in place of Jack, while Jack is still unconscious on the planet, to find the one thing he feels will accomplish this; the one thing that cannot be found again. Meanwhile, the 'real' Jack has returned and is trying to convince SGC that he is who he says he is.

With the Stargate program in danger of being terminated, the team is under pressure to find technology. Visiting a planet where they believe there is a creature that possesses the secret of invisibility, they encounter Apophis and his guards. Both sides receiving mortal wounds, they are aided by the planet's inhabitants, the Nox, a gentle people with a very large secret.

On the planet Argos, Kynthia seduces Colonel O'Neill, which gives him an Argosian lifespan of only a 100 days. As he begins to age rapidly, will the SG-1 team succeed in finding a cure?

SG-1 goes to the planet Cimmeria in search of allies against the Goa'uld. Upon arrival, Jack and Teal'c are trapped in a labyrinth, where the only exit is through Thor's Hammer, a device to destroy Goa'uld, but preserve the host. Daniel Jackson must destroy the device that could someday have saved his wife in order to free his friends.

Daniel Jackson discovers that the Stargate was activated in 1945 and a young professor went through, never to return. Together with his still living fiancée, the SG1 team discover the now aged professor, naked and trapped in a decaying fortress, containing the secrets of an Ancient alliance. Will they be able to rescue him and escape to earth in time?

O'Neill, Carter and Teal'c return through the Stargate shell-shocked and distressed to announce that Daniel Jackson was killed. But Jackson was captured by the last survivor of an aquatic race, who planted false memories in the other members of SG1. Can the team remember and return to rescue Daniel?

On an astronomical black hole observation mission, SG-1 finds a fatal bacterial mass-epidemic on a planet where the natives told then-incredulous Daniel months ago that the coming solar eclipse would bring disaster. They also take back to the Cheyenne Mountain Base a surviving, fairly healthy, orphaned young girl named Cassandra, and awakes Sam's maternal instinct. The Naquadah traces found in her blood turn out to have made her immune, but after she has a seizure they are diagnosed to constitute a huge bomb, somehow triggered by rescuing her; the whole thing must be planned as a 'Trojan Horse' by the Goa'uld. Sam takes the prospect of sacrificing Cassie personally and is prepared to take personal risks.

On their first visit to a new planet, SG-1 finds it subject to totally destructive volcanic activity and saves ten natives, the Tollan, a far more technologically advanced society. Their leader Omoc isn't grateful, nor interested in such a primitive race as the earthlings or any of the 'even more primitive' planets which are prepared to host them. Only one Tollan, Narim, shows an active interest in life on earth, especially in captain Samantha Carter and the cat Schrodinger she gives him, explaining his planet was destroyed after the Tollan supplied an unlimited energy source to a primitive neighboring planet which abused it for a cataclysmic weapon. Meanwhile, the White House authorized NID colonel Maybourne to take charge over the Tollan for military purposes, exactly Omoc's nightmare.

Following a Stargate technical defect, O'Neill and Carter are stranded next to a Stargate in a cave on an icy wasteland. O'Neill is severely wounded and both are freezing. Will the SGC find and rescue them in time?

While collecting artifacts on a distant planet, Daniel Jackson is knocked out after touching a mirror-like object. He awakens in the same room but is unable to locate the other members of SG-1. Assuming that they left without him, he dials up his return home but gets there to find that he is in a different reality. In this world, General Jack O'Neill and Catherine Langford are in charge of the Stargate program; Hammond is a Colonel reporting to O'Neill; and Sam Carter is a civilian scientist working on the project (and also engaged to O'Neill). More importantly, Earth is under attack from the Goa'uld who have already killed over 1 billion people. Carter believes that somehow, Jackson is from a parallel dimension. When Jackson learns the point of origin of the Goa'uld attack, he wants to return to his own universe, believing that his Earth will be similarly attacked.

The Stargate team must justify the project's continuation when a doubtful senator, Head of the Congressional Military Appropriations Committee, comes to review the project's performance.

General Hammond has tried everything to get the Senate's decision to shut down his Stargate program undone, but the President personally refuses to 'commit political suicide': the Stargate will be buried. Daniel's insistence -that the danger for Earth as a whole outweighs everything- convinces his colleagues to ignore Hammond's command and dial the address that the Goa'uld invasion started from in the alternate reality that he visited. They arrive not on a planet but a new, superior type of starship, already launched by hyper-drive. A 'video' proves it belongs to Apophis, who gives command to his son Klorel, whose host is none other than the team's young Abydonian friend, Skaara. Overpowering Skaara seems their best move, while Sam installs explosives in the death glider deck with a 24-hour timer just in case, but the Jaffa manage to liberate Klorel. Jack discovers that the ship goes far faster than expected.

As the Goa'uld attack fleet approaches Earth, all four members of the SG-1 team are taken prisoner. They get help from an unexpected source when Bra'tac, Teal'c's mentor, reveals that he is on board. Apophis has delayed the attack until his son Klorel is revived, giving them some time to prepare. SG-1 has used all of the C4 on one of the two ships but must find a way to dispose of the second. Back at Stargate Command, Lt. Col. Bert Samuels arrives as a Pentagon liaison officer but also reveals a new weapon they have developed. General Hammond is dubious. They begin to transport humans to an Alpha site in order to ensure the continuation of mankind.

While walking through a forest on another planet, Jackson saves the life of a beautiful princess who is about to kill herself. SG1 is taken prisoner, but Daniel is freed by the ruler when he finds out that he saved his daughter. The rest of SG1 is sent to work in the mines for the rest of their lives. Jackson falls in love with the princess, but also becomes intoxicated by frequent use of a Sarcophagus. Will he come to his senses before the rest of SG1 are worked to death?

SG-1 discovers an ancient artifact and brings it back to the SGC. Ariving at the SGC, it becomes active, pins O'Neill to the gate room wall, and unleashes a virus into him.

O'Neill, Carter and Jackson are trapped on Hathor's planet. Teal'c and Hammond go to Chulak to forge a rescue plan and recover the team.

After a cataclysmic meteorite bombardment, Col. Jack O'Neill finds himself stranded on a primitive planet with its Stargate apparently permanently inaccessible.

Ready to go on vacation, O'Neill is beamed away by the Asgard. Thor tells him that Earth is faced with an enemy even worse than the Goa'uld.

SG-1 has to deal with a Replicator infestation on a Russian sub on Earth while Major Carter advises the Asgard about combating the menace in their galaxy.

The SGC is contacted by an advanced and embattled alien human civilization seeking military assistance, but their exact reasons for it become increasingly suspect.

An old love of Teal'c approaches the SGC and the Tok'ra claiming that her Goa'uld symbiote has been convinced to defect with their help.

The SGC learn that the Russians have a Stargate of their own and they need the Americans' help with their problems with it that are affecting them both.

While on an archaeological dig at the original Goa'uld home world, Daniel is captured by a young Unas. He tries to communicate with it and slowly builds a rapport. Meanwhile, SG-1 comes to the planet to find Daniel and they soon realise that some of the SG-team members there may have been taken over by Goa'uld. Will they be able to discover which ones in time to rescue Daniel?

The SG-1 team awake to find they have lost their memories. They believe they are workers in an underground power station. They are told that they are helping to preserve life during an ice age. In truth, they are slave labor to a huge domed city above. When Teal'c starts to recover his memory and is given another amnesia treatment, he forgets his Kelno'reem and starts to die. Will the others recover their memories in time to save him?

General Hammond mysteriously retires from the SGC and a new general is brought in, who breaks up SG-1: Daniel and Sam are scientists, Teal'c is with SG-3 and O'Neill commands a new SG-1. O'Neill tries to convince Gen. Hammond to return, but he finds out that someone ordered Hammond to leave or they would hurt his grandchildren. While the others are occupying the new general, O'Neill tries to find out who that "someone" is. Thereto he must place his trust in the one person he hates most: Maybourne.

In 2010, Robert Kinsey is president of a brave new world since he concluded the alliance with the Aschen, a race discovered by SG-1 which lets humanity enjoy its far advanced science and technology, including a vaccine against aging. Sam is now a civilian scientist, married to ambassador Joe Faxon, whose only worry is failing to get pregnant. When she double-checks the Aschen doctor Mollem's computer with Dr. Fraser, who felt superfluous given superior medicine, they discover human fertility is down 90% worldwide in three years. Sam, Daniel and Teal'c turn to retired general Jack, who always warned against handing over technological control, for a daring plan to turn the clock back like general Hammond did once, sending a message to their past with the exact time of a solar flare, which Sam can calculate using the Aschen computer. Only one ingredient is out of their reach: the GDO device to control the Stargate's iris, which is in the White House. Sam implores her husband Joe to steal it, but he has a secret as well as sincere objections.

When a "chosen" boy found on planet Abydos is brought to SGC, he sends a telepathic message, causing Daniel Jackson's personality to undergo disturbing changes. Will the rest of SG-1 be able to solve the mystery of the boy's origin before he becomes a power-hungry warmonger?

SG-5's Lieutenant Barber commits suicide by jumping into the Stargate shortly after a mission on a planet where a palace abandoned by the Goa'uld about 200 years ago is being studied by Daniel. Soon after, Daniel develops violent mood swings and is committed to a hospital with a neurotransmitter brain condition, presumed fatal after all the other SG-5 members die. Meanwhile, SG-3 has visited the planet, finding only the light installation Daniel reported as particularly fascinating and a human teenage boy, Loran, who hid from Daniel's expedition, but now tells Jack he was left there by his parents, scientific researchers. Back in SGC, Jack also develops symptoms. Sam and Dr. Fraiser conclude that it must be some addiction linked to the light, so when Daniel is nearly terminal Jack, who might not have been exposed too long himself, must bring him back. Jack insists they try turning off the light, and leans on Loran, who is looking for a father-figure; he even gives Teal'c an early "birthday present," but has a dark secret.

Carter decides to inspire a brilliant but difficult Air Force cadet by introducing her to the SGC program.

When the SGC probes a new planet, an alien energy entity there responds by invading the SGC's computer systems, and then Major Carter herself.

Stranded in another galaxy while fleeing their attack on Apophis' fleet proves only the beginning of SG-1's problems as multiple enemies appear.

When SG-1 flees from an expedition with Col. O'Neill and some mysterious team member named Tyler, whom no one else knows about, stranded, the fitness of the team is questioned.

With the death of Omoc, the subsequent sudden Tollan reconsideration of their tech embargo leads to SG-1 suspecting a government conspiracy.

SG-1 makes contact with the Aschen, unaware of that their homeworld is one they were warned previously from the future to be considered off-limits.

When Teal'c is trapped in the Stargate buffer, the team must juggle the technical challenges along with personal, interdepartmental and diplomatic rivalries to rescue him in time.

In a Tok'ra plan to wipe out the Goa'uld, Daniel goes undercover as Yu's servant to release a poison at a meeting of the system lords. Meanwhile a Goa'uld attack on the Tok'ra base leaves the rest of SG-1 with their hands full.

As the Goa'uld summit continues, Daniel finds himself face to face with Osiris. He fools him in the same fashion as he did with Yu, but cannot bring himself to cause the death of Sarah, Osiris's host. He remains to uncover information about the unknown master of Osiris. Lantash, having taken Lt. Elliot as a host, guides the rest of SG-1 in escaping the fallen Tok'ra base.

A large asteroid is discovered on a collision course with Earth.

On an alien planet, SG-1 discovers an inactive android is the only survivor of the destruction of her civilization. They bring her back to the SGC for study and manage to reactivate her. Things take a turn for the worse when she "makes" a replicator bug for Daniel.

To fix a mistake caused by the fake SG team, the real SG-1 must enlist the help of two convicts. The threat of an approaching Goa'uld mothership stresses the repair of the Sentinel.

As Jackson suffers from a fatal dose of radiation, he struggles with the value of his life while his friends deal with the emotional and diplomatic repercussions.

While still dealing with the loss of Daniel Jackson the SGC is contacted by the Asgard who require assistance dealing with Anubis, who seems to have new shield technology that can repel Asgard weapons.

Master Bra'tac arrives with bad news: Teal'c's wife is deathly ill, and Teal'c leaves to be with her. Shortly thereafter, the gate is opened but nothing comes through. Then Carter discovers a very low power signal that is slowly building an overload powerful enough to destroy the Earth.

Anubis' weapon continues to threaten Earth. Various plans are tried until Jonas Quinn suggests something simple that just might work. Meanwhile, Master Bra'tac has discovered the planet from which Anubis is launching the attack. He, Teal'c and Rya'c journey there to put a stop to it.

When SGC detects an Goa'uld ship in orbit, SG-1 is dispatched with Jacob Carter to investigate. They find the ship to be abandoned with no discernible life signs and Sam determines it to be the same used to kidnap Thor. Once on board the Goa'uld vessel, they find that the crew had initiated a self destruct sequence. O'Neill would very much like to salvage the ship despite Jacob's warnings that it could be a Trojan horse. An examination of the computer core reveals that Thor may have been able to introduce a virus but Jacob was right: it's an ambush and the ship soon plunges in the ocean. SGC and the Navy mount a rescue operation.

The SG-1 team travels to the Antarctic science station when the scientists there discover an ancient body in the ice. The age of the ice core samples would indicate that the body predates mankind. As they thaw the body, it comes to life. It's a young woman who they call Ayiana. As Ayiana gains strength, those around her all fall ill having contracted an unknown virus which they believe Ayiana carried. The new arrival also shows healing powers and can seemingly cure any illness just by touch. As she does so however she weakens to the point of death. In the end, only Col. O'Neill remains untreated and SGC seeks the help of the Tok'ra who offer an unexpected solution.

O'Neill's symbiont Kanan drags him to a planet ruled by the Goa'uld Ba'al, where Kanan was undercover. Ba'al captures and tortures O'Neil, whose only hope may lie with - Daniel Jackson?!?

Stargate Command is approached by representatives of Jonas Quinn's home planet seeking military hardware. Their world is divided into three territories and there is a long history of war among them. Jonas' country fears that the other two territories are about to sign a non-aggression pact thus making them vulnerable to attack. In return for arms, they are offering an abundance of Naquadria. SGC isn't about to get involved in what amounts to a civil war but there's another possible outcome when Jonas' one-time professor, Doctor Kieran, tells them of an underground movement ready to overthrow the government and seek out a lasting peace. SG-1 travels to Jonas Quinn's home planet to obtain information on the situation there but not all is as it seems.

SG-1 is providing security for three scientists who are conducting research on a far-off planet. Goa'uld warlord Khonsu arranges to capture the SG-1 team and O'Neill tells Jay Felger, nominally the group's leader, to use the gate and head back to SGC. Felger is quite enamored with SG-1, admiring their exploits and daring-do. Rather than follow O'Neill's orders, Felger and another scientist, Simon Coombs, transport themselves up to the Goa'uld ship. What the scientists don't know is that SG-1's capture is a ruse to allow Khonsu, who is actually a Tok'ra, to pass on information. O'Neill is quite annoyed with the two scientists but their presence proves useful in the end.

Having regained control of the X-303, the SG-1 team finds itself in an unknown part of space. Rescue comes in the form of the Asgard, specifically Thor, who needs their help. The Asgard home world has been overrun by the Replicators and they require SG-1's help as well as the relatively low tech X-303. The Asgard had set a trap for the Replicators and hoped to use a time dilation device that would give them the time they need to find a way to defeat them. The problem is that the Replicators have turned off the device and the Asgard want SG-1 to go in and activate it. They accept the assignment but to meet their objective, O'Neill will face a moral dilemma.

SG-1 brings back an Ancient device, the purpose of which is unknown. When Jonas touched it the device activated. Upon reaching the SGC Jonas sees a large red insect fly into a wall, but no one else can confirm his sighting. The SGC is put into lockdown, but nothing is found. Jonas suspects that the Ancient device is causing his hallucinations, but to his dismay it is set to be shipped to Area 51. When Teal'c and Jack see the bugs as well, General Hammond decides to let Jonas take a crack at deciphering the Ancient text on the device.

Former Colonel Harry Maybourne comes to Jack with a proposition: Jack gets him a presidential pardon and Harry shows them the advanced weapons cache that Simmons was trying to get to. They go through with the deal, but Harry attempts to double cross SG-1. He manages to get through the portal leading to the cache, but with one unexpected item, Jack. They find themselves in a field and Harry's zat is missing. Jack, however, still has his P-90. Harry reveals that they are not at a weapons cache, but rather a utopia. He meant to live out the rest of his life there and believes that there is no way back.

The Russian SG team brings back a man who claims that his people are being experimented on by Nirrti. SG-1 investigate where the experiments are conducted, with the Russian SG team as backup. The inhabitants worship Nirrti as their god and savior from a terrible plague. SG-1 attempts to use the same device Nirrti used on the people to reverse the mutations, but the people turn on them at the arrival of Nirrti.

The US and Russia reveal Stargate Command and its operations to representatives of the other permanent members of the United Nations Security Council.

Teal'c is having strange nightmares featuring Apophis in which he is human and a firefighter with the rest of his team alongside him.

On a routine mission, SG-1 encounters a civilization desperate to be freed from the clutches of a Goa'uld. While on the planet, Jonas falls ill and is suspended from active duty. His mysterious illness is diagnosed as a brain tumor but gives him the unbelievable ability to glimpse the future, a future where O'Neill and SG-1 are walking into a trap!

Riding in the elevator in the SGC, O'Neill is visited by Daniel Jackson who needs his help. Daniel tells him that Anubis is headed for Abydos to search for something called the Eye of Ra, a relic that would make Anubis all-powerful. It's essential that SG-1 go to Abydos and secure the Eye but no has seen it - including Daniel - nor has anyone ever been able to find it. On the planet they see their old friend Skaara and with Daniel's help locate the Eye. They also find a tablet that speaks of a lost city of the ancients. When Anubis and his troops land in force there is little anyone can do to stop them. In the end it's left to Daniel to decide if he will try to stop Anubis - thereby breaking a cardinal rule of the Ancients.

A group of nomads on an alien planet find Daniel Jackson naked in the middle of ruins and take him in. Jonas translates the tablet Daniel said was important and discovers that it describes the last city the Ancients were building before the plague. He surmises that the list of addresses Jack put into the computer while storing the Ancient data were Ancient outposts in temporal order. Thus the last of the addresses should be the "City of the Lost". SG-1 visits the planet and happens upon the nomadic people, now inhabiting the ruins of the Ancient city. There they find Daniel, but discover his memory is gone. They must recover his memories in order to discover the secret to defeating Anubis.

Anubis's super weapon has been put out of commission, but Yu's fleet has been diverted to the other side of the galaxy by Yu himself, allowing Anubis to escape into hyperspace. Jonas has been captured by Anubis and Daniel is still aboard Anubis's ship, evading capture. Anubis uses the mind probe on Jonas, learns of Naquadria, and begins his attack on Kelowna. The Kelownans seek aid from the SGC. Jack and Sam arrive on Langara to discover that the Kelownans have given Anubis Naquadria in order to secure their safety. They communicate with Daniel who is attempting to free Jonas. Teal'c has convinced Yu's first prime to seek a new leader of the System Lords, Ba'al.

In a firefight with Jaffa, Teal'c takes a staff blast to the gut. Without his symbiote, he cannot regenerate as he once did. Daniel feels that he cannot remember something important, so he goes searching through the logs for any sign of his lost knowledge. Teal'c expresses his feelings that the Tritonin has made him weak.

SG-1 investigate a seemingly idyllic and subtly advanced human colony sheltered inside an energy dome on an otherwise inhospitable planet.

While exploring a crashed alien ship full of passengers in cryostasis, an alien force has downloaded a number of their consciousnesses into Daniel.

When an SG geological exploration mission runs into deadly conflict with an indigenous Unas clan, Daniel gets Chaka to help seek an accord with it.

To save his job, Dr. Felger tests a new virus on the Stargate Network to help control it and it ends up disabling it instead.

At the new Alpha site, Sam Carter and Selmak (the symbiote carried by Jacob Carter, her father) are working on a new weapon to defeat the Anubis superdrones when the planet is attacked by a fleet of Goa'uld ships. Carter escapes with the prototype weapon before the base auto-destruct is activated but finds herself being pursued by a superdrone.

The president has asked that a documentarian go to SGC to create a film about its operations. His arrival is unwelcome to most and he begins to clash with the base personnel. Nevertheless, he conducts his interviews with SG-1 and the scientists in the employ of SGC. Meanwhile, an off-world SG team finds the remains of an Ancient city.

The documentarian still a thorn in their side, SGC encounters an unforeseen predicament. With half of SG-13 off-world engaging enemy Jaffa, SG teams 1, 5, and 7 go in as backup. In the midst of heavy fire, O'Neill takes a staff blast to the chest. Many deaths from the encounter hit SGC hard and Senator Kinsey orders a full investigation into the matter.

The newly inaugurated President of the United States is briefed by the Head of the Joint Chiefs of Staff on the Stargate program. Former Senator, now Vice President, Kinsey attempts to get his running mate to back his policies for the program, but the president decides to look into the situation himself. Kinsey gets Richard Woolsey to convince the president of his agenda.

Vice President Kinsey briefs Dr. Weir on the Stargate program before her meeting with the president. SG teams 1, 3, and 5 go off-world to attempt the extraction of a newly found Ancient repository device. Upon arriving at the location of the device, SG-1 comes under fire from Goa'uld ships. With no other way to disallow Anubis from claiming the knowledge for himself, Jack submits himself to the dangerous device.

With Jack having the knowledge of the Ancient repository once again in his mind, he and Daniel attempt to unearth the location of the Lost City of the Ancients. Bra'tac, bringing with him the news of an impending attack on the Tau'ri by Anubis, takes Teal'c to help him acquire ships and warriors for the defense of Earth. Dr. Weir attempts to cope with the overwhelming nature of her new job, while also dealing with the unrelenting ego of Vice President Kinsey.

In a last ditch effort, O'Neill activated an Ancient weapon in the Antarctic to defeat Anubis. With Jack still in stasis in the Ancient outpost buried in Antarctica, SG-1 tries to contact the Asgard. Meanwhile their new leader, Dr. Elizabeth Weir, tries to decide what to do about a request for peace talks from the Goa'uld System Lords.

The Asgard fleet has managed to destroy the Replicator ship, with Carter aboard, but cannot contain the debris. Talks break down with the System Lords, ending in a Ha'tak being dispatched to test Earth's new defensive capabilities. The Prometheus waits to engage the incoming enemy, but Thor arrives in the Daniel Jackson, with Teal'c aboard. They enlist the help of Daniel and Jack, still in stasis, to remove the threat of the replicators to the new Asgard homeworld.

As the new head of the SGC, General O'Neill is beginning to feel the weight of his load, and he starts to have second thoughts about the whole idea, questioning his own competency.

The discovery of the Stargate creates a war between two nations on the planet Tegalus with Daniel in the middle of it.

Dr. Lee is adapting a virtual reality chair for use as a training device. Teal'c thinks its current scenario is all too easy and agrees to work with them to make it more realistic. He enters the game scenario and is quickly "killed" at which point the chair shocks him. Lee says it must be part of its basic construct. As the scenario resets - it's an invasion of SGC by Goa'uld - Teal'c is repeatedly killed and shocked putting him in danger. The computer program is set up to learn after each scenario and the challenge for Teal'c increases at every turn. Daniel volunteers to enter the game as well to see if together they can find a way out.

Having obtained permission to live off the base, Teal'c rents an apartment, telling neighbors that he has recently arrived from Mozambique. He's under orders to keep a low profile but can't seem to help himself when it comes to helping his neighbors. He helps one who is about to be assaulted by three thugs, but it's his next-door neighbor who seems to need assistance. Krista is having problems with her boyfriend, Doug. Teal'c soon realizes that Doug is beating her and warns him that should he hurt her, Teal'c will kill him. It all becomes very difficult when Doug is found dead in Krista's apartment. Daniel Jackson soon after receives an offer - translate a Goa'uld text, and he will get ironclad evidence that Teal'c is innocent. Meanwhile, Carter is shocked when her boyfriend Pete Shanahan tells he asked for a transfer to the local police department and asks her to marry him.

Teal'c is unhappy with his son's plans to marry. Ishta arrives bringing news that Hak'tyl may be compromised. Complications arise when O'Neill allows Hak'tyl to inhabit SGC until a new homeworld is found for them.

When the Stargate gets beamed out of SGC in the middle of the night, Teal'c is stranded off-world. Dr. Jackson and Colonel Carter attempt to recover the gate.

The replicator Carter and the real Carter work together with the disruptor signal. The replicator has a different plan.

General Hammond returns to SGC to take Dr. Jackson with him on a trip to Atlantis onboard the Prometheus. In the middle of their trip, the Prometheus picks up a distress signal and Hammond decides to investigate. Things get sticky when a Kull Warrior takes control of the Prometheus, leaving Hammond and his crew, minus Daniel Jackson, behind in a damaged Alkesh.

Ex-Vice President Kinsey comes to Jack informing him of the Trust's activities including what seems to be a plan for the Russians to reclaim the Stargate they lent to the United States. He decides to use Kinsey as their inside man with the Trust. Kinsey wears a wire for his meeting with the Trust to set up a meeting with a high-ranking Russian general. The plan goes south when the signals get jammed just as the Trust makes an astounding revelation to Kinsey and they beam out.

After a long absence, Jacob Carter returns to the SGC to tell Jack that the galaxy is under threat of takeover by the Replicators. The Goa'uld are under attack from the Replicators and are quickly being eliminated. Ba'al's armies are being destroyed and he arrives at SGC to suggest they work together to defeat their common enemy. Carter's doppelganger, RepliCarter, is leading the attack and she has kidnapped Daniel Jackson in the hope of learning of any weapons the Ancients may have created that could defeat them. Jackson gets help from an unexpected source - the Ancient, Oma Desala - or so he thinks.

Sam and Jacob are on the planet Dakara trying to configure the Ancient's device to destroy the Replicators once and for all, helped partly by Ba'al and Daniel, who succeeds in freezing the Replicators by manipulating Carter's duplicate.

Daniel finds himself in a strange time and place - a diner where Oma is working as a waitress. She gives him a clear choice - he can choose to die or to ascend but if it's the latter, he will not be able to help his friends fight Anubis, who has yet to be disposed of. He strikes up a conversation with another patron, Jim, who has his own take on the situation. Meanwhile, Sam decides the time has come for her fiancé to meet her father, Jacob. Jacob is not well, however, something he has kept from Sam for several weeks. After Pete surprises her - he thinks he's found the perfect house for them - Sam realizes she has to come to grips with her feelings for someone else. Teal'c and Master Bra'tac have information that Anubis may be gathering what remains of his forces for an attack on Dakara.

With a new commander of the SGC comes a new leader of SG-1, Lt. Col. Cameron Mitchell, a former fighter pilot who flew an F-302 in the battle over Antarctica. However, he is deterred by the fact that all the other members of SG-1 are leaving for other ventures: Teal'c to manage the Jaffa Nation, Carter to Area 51 for alien R&D, and Dr. Jackson to Atlantis as an Ancient expert. Mitchell endeavors to keep the members of SG-1 for himself, but they are increasingly tough to convince.

Daniel and Vala have used the Ancient device to inhabit the bodies of people in the Alterans' home galaxy. They have been taken by a Prior of the Ori to meet the Doci, one who speaks with the Ori, their gods. Daniel surmises that the Ori are what the Alterans who became the Ancients left behind and have ascended in a similar fashion, but without the restrictions.

Vala returns to the SGC upon having been separated from Daniel for a little under an hour. The effects of the bracelets have not diminished even though they have been removed. In order to get the effects reversed, Mitchell, Jackson, and Vala must deal with many people that Vala has used over the years to gain favors.

Vala leads SG-1 to a planet which the Priors have visited with a plan to keep them from worshiping the Ori. Once there she reveals that the symbiote that once held her ruled over this planet. She feels that keeping them in allegiance to her will hinder the spread of Origin to this world.

A Prior of the Ori has established an ever-growing forcefield on a Jaffa-controlled planet called Kalana. A minor Goa'uld named Nerus, who engineered the multiple Gate connections required for the defeat of the Replicators, comes to the SGC with information on the event and offers his help.

Following the death of a Jaffa on Earth and the disappearance of a prominent businessman, SG-1 starts an investigation into what remains of the Trust and into the actions of the Jaffa Nation. They discover that Ba'al is hiding on Earth after losing his forces to the Jaffa and that the Jaffa are secretly attempting his capture.

SG-1 investigates a planet that is said to be the home of the Warriors of Sodan, a legendary tribe of Jaffa said to have not served the Goa'uld in 5,000 years. In an encounter with the warriors, Mitchell deals a deadly blow to one of the Sodan and is captured and taken to their village. There he awaits a battle to the death as punishment for his crime.

SG-1 finds a Goa'uld-Human hybrid in stasis in an abandoned Goa'uld lab and take it back to Earth to study, where they learn it was created using Anubis' DNA.

The Ori unleash a deadly plague on Earth, prompting a powerful ally from SG-1's past to come to their aid.

The plague continues to spread among the US population and the President has quarantined the nation. Teal'c is pleading with the Jaffa High Council to reject Origin, but Gerak arrives, having been transformed by the Ori into a Prior. Cameron and Daniel seek the blood of the Prior that caused the plague in order to cure it, but have once again been captured by the Sodan.

On another planet, Mitchell is placed under arrest for the murder of a scientist.

SG-1 returns early from a mission only to realize that they and Gen. Landry aren't on the same page as far as the the mission they've just completed is concerned. The confusion is quickly resolved when the "real" SG-1 returns at the correct time. Dr. Lam examines them all and concludes that they are identical and thinks they might be clones. Sam however thinks they may have come from a parallel universe as the result of the black hole they created when they destroyed the Ori beachhead. As more SG-1 teams arrive from other alternate universes, one of them includes Dr. Fraiser and another includes the Tok'ra Martouf. It's left to Sam and Martouf to find a way to send them all home.

A contact within the Rand Protectorate comes to Earth with news that the Ori have given his people a superweapon to use against the Caledonian Federation in exchange for their conversion to Origin. SG-1 plans to turn the people from their newfound religion and destroy the superweapon.

While investigating the source of an addictive corn-like crop, SG-1 becomes involved in a firefight. They are forced to fall back to the gate, but as Daniel is dialing both the Stargate and the DHD are beamed away.

SG-1 is tasked to accompany members of the International Oversight Advisory, including Richard Woolsey, on a tour of the Gamma site. The visitors are suitably impressed but everyone is put in danger when a carnivorous insect escapes from the lab. The base is locked down and no one is allowed to travel through the gate. The bug is linked to the Ori - it's appeared on several planets that they've visited - and Daniel thinks it may be their follow-up to the virus. SG-1 and the IOA visitors take refuge in a cave, but Gen. Landrey is left with little choice but to flood the planet with a deadly neurotoxin to destroy the bugs. SG-1 looks for away out before that happens.

Sam manages to activate an Ancient device they found at the Glastonbury site and she and Mitchell are shifted into a phase that makes them invisible to everyone. Daniel soon figures out just what is going on but Dr. Lee's proposed solution sends Daniel to the same plane as Sam and Mitchell. There he is able to translate information explaining that Merlin had created a weapon against the Ori - and provides a gate address where it can be found. Meanwhile, Teal'c travels to a Jaffa planet that has sent out a distress call. The two events are related.

Using the Ancients' communication technology, Vala, who is in the Ori galaxy, contacts the SGC. She tells them that after being sucked into the wormhole she awoke in a bed in a village much like the one she and Daniel had visited when they used the communication stones. The locals think she fell from the sky - a gift from the gods - and befriends the gentle Tomin, a devout follower of the Ori who has a bad leg. Vala has two pieces of information for the SGC: first, she is pregnant though insists that she didn't have sex with anyone; and second, the Ori have been building a fleet of ships and building up its army. Meanwhile, Colonel Chekov advises General Landry that the Russians will not be renewing their working agreement with the United States and will be taking their Stargate.

As the Ori invasion continues, Vala and Daniel must deal with their leader, Vala's young daughter, who is rapidly aged by the Ori to serve their purposes.

While Daniel and Vala search for Merlin's anti-Ori weapon in Atlantis' library, Mitchell, McKay and Carter try to to dial the Ori Supergate in the Milky Way.

The SGC is approached by an Al'kesh bomber which lets itself be taken down, so they can capture Ba'al, who offers to exchange the necessary information to find Merlin's weapon for human help to eliminate his clones, which want to kill him. They mistrust his story, as does NID Agent Malcolm Barrett, who, however, fails to take over the investigation. Since the captive might actually be a clone, several missions to different planets retrieve and capture all clones, but which is the real Ba'al, and what are his true intentions?

Martin Lloyd seeks out SG-1 for assistance when his failed TV show based on the real Stargate program becomes a feature film.

SG-1 is caught in the middle of a war after the Jaffa use a powerful weapon to kill 10,000 Ori followers.

Vala is kidnapped by agents of the Trust who are trying to find an ancient treasure when an accident causes Vala to forget who she is.

Cameron Mitchell must go undercover inside the Lucian Alliance to find the location of the hijacked Odyssey.

SG-1 blows up three transport ships in a row; Netan puts a price on their heads. General Landry grants the team members spare time on Earth. Daniel spends it researching in a library, where he meets a bounty hunter who tries to seduce him, then switches to her handgun... but is taken out by a bus. Sam gives a lecture on Air Force technological progress together with Dr. Bill Lee; a sniper nearly misses, but is taken out with an experimental weapon they'd brought along to demonstrate. Teal'c is injured by surprise at a Jaffa camp and successfully traps the killer to try again. Cam goes to his Kansas high school reunion and Vala succeeds in making him bring her along, pretending to be his accountant and partner. His still sexy former flame he'd believed out of his reach, Amy Vandenberg, is initially scared off by Vala, but, divorced and interested, explains she still has a secret crush on him. Alien bounty hunter Odai Ventrell assumes numerous classmates' appearances to kill him. Vala's failed rescue gets them both captured publicly, so he threatens to kill off reunion guests unless the other SG-1 members take their place, but they trick him using Chimera technology; they hope Netan's failure to eliminate them will rekindle the power struggle and Odai reacts surprisingly.

Teal'c and Bra'tac are among the numerous victims -though only wounded- of several bomb attacks killing 32 men at a summit in the Jaffa settlement Dar Eshkalon. As soon as physically able, Teal'c swears to avenge them personally, suspecting the honor-less, ambitious warrior Arkad; General Landry refuses to sanction a killing mission without solid proof, but cannot stop Teal'c from going it alone. Bra'tac explains Arkad's sinister past to Daniel, including the possibility of murdering Teal'c's mother. Information from the resistance on another planet indicates Arkad is in league with the Ori and plans to attack Earth. Arkad comes to meet General Landry, offering to help defend Earth against the Ori, denying any part in the bombings, while defending Origin, incriminating a Jaffa sect. SG-1 is now ordered to find and stop at all cost Teal'c, who is using torture. But Teal'c, committed to killing Arkad, reaches his place, but is wounded, captured, and made to duel Arkad after it is confirmed he had killed Teal'c's parents.

Stargate Command gets a video message from Vala's extremely unreliable father, Jacek, on the planet Robak; he claims to know about the late Arkad's plans to attack and blow up Earth, even about the several cloaked, Naquadah-laden cargo ships in orbit, and offers details in exchange for sanctuary. General Landry asks Dr. Lam to help him resume contact with her mother, Kim, his ex-wife. Even after the cargoes are found and blown up, Vala abhors her dad's entry. The general asks her to go easy on him, realizing that he, too, neglected his daughter because of his career, even if Jacek's neglect was just criminal. When Cam and Daniel go tell Jacek he shouldn't scam people, he tricks them into talking to Vala for him. Vala goes over just for catharsis, telling him she's through picking up the pieces of his tricks, and he certainly keeps scamming - as Daniel also finds - even with Terak, a Jaffa from an escaped cargo ship, who hopes to sell the Naquadah. When they are apprehended, Jacek promises to help track it and override the rigging of the cargo ship. The Jaffa wait for Jacek and Vala, intending to eliminate them now that Terak is gone, but SG-1 saves them. Since there never was an override, Jacek cheerfully flies away alone in the cargo ship, ignoring that his treachery was anticipated: it's a decoy.

General Landry accompanies SG-1 on a mission to collect the knowledge of the Asgard. When the Ori show up, however, Sam is forced to evacuate the crew. Landry and SG-1 stay aboard, but are stuck helpless in a time dilation field for decades.

When the Stargate gets beamed out of SGC in the middle of the night, Teal'c is stranded off-world. Dr. Jackson and Colonel Carter attempt to recover the gate.

As the new head of the SGC, General O'Neill is beginning to feel the weight of his load, and he starts to have second thoughts about the whole idea, questioning his own competency.

The president has asked that a documentarian go to SGC to create a film about its operations. His arrival is unwelcome to most and he begins to clash with the base personnel. Nevertheless, he conducts his interviews with SG-1 and the scientists in the employ of SGC. Meanwhile, an off-world SG team finds the remains of an Ancient city.

As the Goa'uld attack fleet approaches Earth, all four members of the SG-1 team are taken prisoner. They get help from an unexpected source when Bra'tac, Teal'c's mentor, reveals that he is on board. Apophis has delayed the attack until his son Klorel is revived, giving them some time to prepare. SG-1 has used all of the C4 on one of the two ships but must find a way to dispose of the second. Back at Stargate Command, Lt. Col. Bert Samuels arrives as a Pentagon liaison officer but also reveals a new weapon they have developed. General Hammond is dubious. They begin to transport humans to an Alpha site in order to ensure the continuation of mankind.

SG-1 finds a Goa'uld-Human hybrid in stasis in an abandoned Goa'uld lab and take it back to Earth to study, where they learn it was created using Anubis' DNA.

The SGC is contacted by an advanced and embattled alien human civilization seeking military assistance, but their exact reasons for it become increasingly suspect.

On an alien planet, SG-1 discovers an inactive android is the only survivor of the destruction of her civilization. They bring her back to the SGC for study and manage to reactivate her. Things take a turn for the worse when she "makes" a replicator bug for Daniel.