The Stargate SG-1 team discovers what they believe to be the remnants of the lost city of the Ancients – the originators of the Stargates and Stargate Command launches an investigation to find the mythical city of Atlantis. Situated in the distant Pegasus Galaxy, it's farther than any Stargate team has ever traveled. With only enough power to make a one-way trip, a new team, headed by civilian Dr. Elizabeth Weir, is formed and travels through the gate to this unknown galaxy. There, they discover the marvels of the lost city of Atlantis.... and encounter a sinister new enemy.