While searching for the Lost City of the Ancients on a distant planet, SG-1 is stunned to find Daniel Jackson alive and in human form but stripped of his memory. O'Neill convinces Daniel to return with them to the SGC, where he is reinstated for a daring mission to destroy Anubis' powerful new super-weapon!
As SG-1 searches for an Ancient artifact which they hope can defeat the armies of the Ori, they learn more Ori ships are about to be sent through the Supergate to launch a final assault on Earth. Daniel discovers that the artifact, the Ark of Truth, may be in the Ori home galaxy, and SG-1 embarks aboard the Odyssey to find it, and pre-empt the attack. The IOA has a plan of their own and SG-1 ends up in a distant galaxy fighting two powerful enemies.
While SG-1 attends the execution of Ba'al, the last of the Goa'uld System Lords, Teal'c and Vala inexplicably disappear into thin air. Carter, Daniel and Mitchell race back to a world where history has been changed: the Stargate program has been erased from the timeline. As they try to convince the authorities what's happened, a fleet of Goa'uld motherships arrives in orbit, led by Ba'al, his queen, Qetesh (Vala), and his first prime, Teal'c. SG-1 must find the Stargate and set things right before the world is enslaved by the Goa'uld.