Combat engineers from Atlantis work against the clock to rescue four of their colleagues who are now trapped in the rubble of Michael's medical compound. With Michael en route, they quickly locate McKay and Major Lorne but Sheppard and Ronon are far deeper and their rescue is not assured. When Michael's ship arrives, they decide to try to rescue Teyla who is in labor and close to giving birth. When it's all over, Col. Carter is recalled to Earth for a performance review but Richard Woolsey has some bad news for her.

Dr. Carson Beckett is removed from stasis because he's the only one who can find the antidote to a mysterious virus that has incapacitated base personnel, beginning with Dr. Jennifer Keller.

Ronon is abducted by a Wraith who tries to brainwash him.

An empty Daedalus is found orbiting the planet. The team goes to check it out and they are transported to an alternate universe.

A group of beings stranded in sub-space seek help from Atlantis to return to normal space. But their outrageous claims and erratic behavior strains the trust of their benefactors and forces a painful solution.

Rodney is infected with a deadly illness known as "second childhood" which diminishes his mind capabilities and makes him lose his memory gradually.

Sheppard and Beckett battle zombie-like, Wraith-engineered mutants with a team of the best and brightest female SG members.

Teyla risks her life on a daring mission aboard a wraith hive ship.

Jennifer, Ronon and Rodney find themselves in the middle of a Wraith hunt when Jennifer is kidnapped by a runner, Kiryk, to help him with a humanitarian mission.

Dr. Daniel Jackson comes to Atlantis in search of a lost Atlantian room. The discovery reveals a new race. Daniel and McKay are kidnapped by the new race and are forced to finish a device which may kill the Wraith. Todd feels betrayed and takes the Daedalus.

The new race that stole the device, not to mention Rodney and Daniel, turns out to be an old one meaning very old and well known to the human race. With an ancient grudge to settle, they force Rodney to activate the device against the Wraith with a side effect that could kill millions throughout the galaxy. That makes the Wraith mad so they abscond with the Daedalus to retaliate. Once again we lowly humans have to take control of a messy situation to keep the master races from wreaking havoc in the galaxy.

The Atlantis team endeavors to thwart Wraith plans to either find a cure for the Hoffan drug (which makes humans deadly to Wraith feeding on them) or exterminate all those infected.

Sheppard and his team are lured to a planet and are soon put on trial for crimes against the people of the Pegasus galaxy. In flashbacks, the three judge tribunal recounts the indictment against them including the re-awakening of the Wraith and the various missions where at least a few, if not more, innocent bystanders were killed. Sheppard does his best to argue that on balance, fewer were killed by their presence than would have been the case if they had never been there. A least one of the judges is clearly determined to find them guilty while a second seems far more sympathetic. It's left to Richard Woolsey, who has now joined them, to plead the rest of their case. A lawyer by profession, Richard clearly knows how the game is played and focuses on that third judge.

When the power is shut down and most of the inhabitants are locked out of key controls, it is apparent that Atlantis has been taken over by an off-world group, soon identified as Michael and his hybrids. He is after Teyla's newborn child who is key in his quest to gain control of the Pegasus galaxy. While Sheppard and McKay try to get their hands on a jumper to launch an attack, Ronon and others who were taken prisoner by Michael during his initial invasion launch reprisals of their own. When Teyla manages to get away and hide, Michael gives her a simple choice: surrender herself and her child to him or he will use the city's self-destruct mechanism to kill everyone.

Radek discovers an alien device that Rodney finds holds serious surprises. Sheppard runs into a reincarnated Acastus Kolya who plans to attack Atlantis. An IOC representative arrives to replace Woolsey who receives advice from a mysterious woman.

Rodney finally invites Jennifer on a date; to attend a science conference with him. But petty jealousies arise at the conference that have to be suppressed when a proposed solution for global warming has potentially lethal side effects.

A Wraith cruiser arrives at Atlantis and is strangely uncommunicative.

An alien mind takes up residence in Jennifer's body and seems as confused as her colleagues are by her erratic behavior. Which begs the question; where is Jennifer?

The killings of a Wraith in Las Vegas are investigated by Detective John Sheppard - who knows nothing about life-sucking aliens from another galaxy.

A hive ship turbo-charged with a ZPM has received the Wraith's message from a alternate universe containing the location of Earth. The ship is now heading for Earth.