A new Stargate team embarks on a dangerous mission to a distant galaxy, where they discover a mythical lost city -- and a deadly new enemy.

Sheppard tries to convince Weir to mount a rescue mission to free Colonel Sumner, Teyla, and the others captured by the Wraith.

Dr. Daniel Jackson arrives in Atlantis to investigate a hidden lab left behind by the rogue Ancient scientist Janus. Their discovery has attracted the attention of a mysterious group of aliens, who infiltrate the city. Meanwhile, "Todd" and a delegation arrive on the Daedalus to bring forward Dr. Jennifer Keller's gene therapy.

As Dr. Rodney McKay and Dr. Daniel Jackson is held prisoner by the Vanir, they make a startling discovery about who they really are. Meanwhile, "Todd" and his Wraith hijack the Daedalus to find and destroy those who activated the Attero device. The Travelers arrive and Lt. Colonel John Sheppard must help them get to the planet before "Todd" uncovers a way to discover the device for good, even if it means sacrificing McKay and Jackson's lives to do so.