When SG-1 discovers what they believe to be the remnants of the Lost City of the Ancients - the originators of the Stargates - Stargate Command launches an investigation. A new team of explorers, headed by civilian Dr. Elizabeth Weir, travels to the distant Pegasus galaxy, where they discover an advanced but deserted city on the ocean floor, a group of nomadic humans...and a deadly enemy that feeds on human fear!