Episode 55 of "Stargate-SG1"
s03e11 Past And Present

SG-1 travels to a planet whose inhabitants seem to be suffering from mass retrograde amnesia. They have no memory of their lives before the unknown event they call the "Vorlix", and report that their elders and children are missing. The planet faces complete devastation unless the people's memories can be restored. The inhabitants introduce Ke'ra, a brilliant and personable young woman who has come to be the leader of her people. She and Daniel Jackson develop a mutual attraction. Ke'ra returns to Earth with SG-1 in hopes that her existing research on the Vorlix may help them find a cure. But as the investigation progresses, SG-1 begins to suspect that Ke'ra may not be who or what she appears.