S1, E19: While exploring an alien Stargate complex on P3R233 a world that appears to have been destroyed by the Goa'uld Daniel Jackson discovers a slab that when activated turns into a shimmering mirror. He touches the mirror and gets a mild jolt but thinks nothing of it until he returns through the Stargate. Then he finds himself in an alternate reality a place that looks like Earth but where nothing is quite as it was. The most distressing difference is that this world is under attack by the Goa'ulds who have wiped out half-a-billion people and are about to capture the Stargate Command. O'Neill faces-off against Teal'c who in this reality is still loyal to the Goa'uld and Daniel tries to escape through the Stargate with information that may save his world from the fate of this alternate reality.