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, hundreds of Goa'uld motherships arrive in orbit, led by Ba'al, his queen Qetesh (Vala), and his first prime, Teal'c. The remaining SG-1 members must find the Stargate and set things right before the world is enslaved by the Goa'uld.