When a secret base abandoned by the Ancients — the original builders of the stargates — is found buried in the ice of Antarctica, the Stargate Atlantis team is recruited for the most daring stargate mission yet: a one-way expedition to the distant Pegasus galaxy.

There the Stargate Atlantis team encounters a number of primitive human civilizations ... as well as The Wraith, a sinister new enemy that threatens human life everywhere.

The Stargate Atlantis mission is headed by Dr. Elizabeth Weir (Torri Higginson), a specialist in diplomatic relations. Her political savvy is balanced by the go-with-your-gut bravado of her military counterpart, Maj. John Sheppard (Joe Flanigan), a courageous and gifted pilot. Rounding out the team are Lt. Aiden Ford (Rainbow Sun Francks), the enthusiastic young officer who becomes Sheppard's second-in-command; and Dr. Rodney McKay (David Hewlett), a clever and quick-witted astrophysicist with previous experience at Stargate Command. The team is befriended by Pegasus galaxy native Teyla (Rachel Luttrell), a beautiful young leader among the Athosian people, with whom the Atlantis team forges an uneasy alliance against The Wraith.
In a special guest starring role, sci-fi favorite Robert Patrick appeared as Col. Marshall Sumner in the two-hour Atlantis premiere event.

New faces join the team in the second season. Most notable among them are Ronan Dex (Jason Momoa), a human native to the Pegasus galaxy who has fought the Wraith for seven years in defense of his planet. And from Earth comes Col. Steven Caldwell (Mitch Pileggi), the commander of Earth's newest intergalactic battle cruiser, the Daedalus.