When an operative of the Trust plants a bomb in Atlantis, the team must find a spy within their own ranks before the Wraith arrive and discover the city.

Floating in deep space with the city's protective shield failing, the team must do all they can to keep Atlantis alive. A radical injury threatens Dr. Weir's life.

Colonel Sheppard and his team embark on a risky mission to steal a Z.P.M. power module from the Replicators -- but must rely on a compromised Dr. Weir to succeed.

While on personal leave on Earth, Sheppard and Ronon learn that scientists have engineered a human-form Replicator -- who is now on the loose.

Teal'c visits Atlantis to counsel a headstrong Ronon, who is up for review by the I.O.A. But the two must work together when the Wraith invade the Midway space station in order to reach Earth.