The SG-1 team are kidnapped by an old nemesis who requires their skills to open a mysterious subterranean chamber. But the chamber has a strange effect on all who approach it, and before long the entire team is suffering hallucinations. When a Goa'uld, who is impersonating the god Sebek, takes control of Dr. Daniel Jackson's body to complete his work, the team must act to stop him before he gains control of a powerful and deadly weapon which could change the balance of power in the galaxy forever.