Synopsis by Hal Erickson
The Quantum Mirror, introduced in the first-season Stargate SG-1 installment "There But for the Grace of God", is brought into play in this episode. The mirror leads to an alternate-reality Earth, in which deceased Stargate Command officer Major Kawalsky (Jay Avocone) still lives and SG-1's Captain Samantha Carter (Amanda Tapping) is a Major. When the "other" Earth faces invasion from Goa'uld, SG-1 races to the rescue. But because of the peculiarities which separate the two worlds, only one of the Samantha Carters has a chance for survival.