SG-1 teams up with a Russian task force to investigate the disappearance of a Russian SG team on P2X-338. They discover that the Russian SG team released a creature that killed Marduk, a Goa'uld, in his sarcophagus. SG-1 must trust their Russian partners in order to escape the ziggurat alive.

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.

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.

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

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.

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.

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.

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.

Based on the information Vala gave them, SG-1 travels to the planet where Merlin may have hidden his secret weapon to defeat ascended beings. There they find an appropriately medieval village and learn that Merlin kept a library there. The locals have never been inside owing to a curse on anyone who dares enter, but SG-1 finds a way in. Once inside, they find a secret chamber that may reveal the location of the weapon. The SGC, meanwhile, has located the Ori's Supergate. Sam's attempt to get control of it is too late, and four Ori ships make their way through. In the ensuing battle, much of Earth's fleet is destroyed, and the future of several SGC members is left in doubt.

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.