Stargate SG-1 - Season 0, Episode 8 - Continuum

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.