SG-1 learns of a new Prior spreading the word of the Ori in a more humane way then ever before and decides to investigate. When the new prior turns out to be Daniel Jackson (Michael Shanks) the team elects to save him even though it's very likely a trap by Adria (Morena Baccarin).
Transported and held captive on the Odyssey Daniel explains his becoming a prior is all part of an elaborate plan that he and Merlin, who is still partially in control of his consciousness, have devised to trap Adria and the Ori. Though his story seems to honestly prove how he gained Adria's trust only to use Merlin's device against her, his plan requires SG-1 to close the wormhole that is blocking the Supergate. With the Supergate functional there would be nothing stopping the Ori from sending their armies through to earth's galaxy. Whether or not they aid him with his potentially catastrophic plan becomes mute when the IOA decides Jackson poses too great a risk and must be killed.
Col. O'Neill (Richard Dean Anderson) not willing to let his friend be sentenced to death works with the SG-1 team to find a way to finish Merlin's weapon and send it through the gate to destroy the Ori. But when Jackson is able to escape imprisonment and hijacks the Odyssey along with Col O'Neill it appears that his plan was really just a way of delivering SG-1 and the finished Merlin device to Adria.