Season One
While SG-1 explore P3R233, Daniel touches a mysterious mirror and finds himself alone. He dials the gate and returns to what he thinks is the SGC, but he is confronted by a Colonel Hammond.
Daniel has crossed over into an Alternate Universe.
Like our Earth a team travelled to Abydos and destroyed Ra but in this universe Teal'c never left the service of Apophis and is part of an assault on Earth.
Sam Carter is not in the military and engaged to General Jack O'Neill.
Daniel has to make them believe his story and find a way to return to his SGC and warn them of the impending Goa'uld attack.
First episode in a four Part story arc.