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.

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.

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.

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.