Conclusion. Col. Caldwell (Mitch Pileggi) reinforces the beleaguered Atlantis team as the Wraith mass for another assault. Meanwhile, a seriously wounded Lt. Ford's abnormally rapid recovery causes further worry as his behavior turns erratic.

McKay discovers that a sinister artificial intelligence has infected the computers of the Daedalus after circuitry malfunctions result in the death of two scientists.

The team's discovery of a Wraith's mutilated remains during an expedition leads to an encounter with local warrior Ronon Dex (Jason Momoa), who has information about the missing Ford.

A new security officer (Jaime Ray Newman) is trapped inside McKay's body with its unwilling host after Dr. Zalenka (David Nykl) botches the pair's transportation from a Wraith vessel. Also, Sheppard petitions Weir to allow Ronon to join the Atlantis team.

The team's suspicions are aroused when they arrive on the technologically advanced world of Olesia, where the population appears to be immune from the ravages of the Wraith. McKay and Sheppard soon discover why when their puddle jumper crash-lands on a secluded island.

McKay tries to harness an energy source hidden within a monolith constructed by the Ancients on a planet previously believed to have been destroyed by the Wraith. But his obsession with tapping the structure's power has deadly consequences.

A synthetic virus created by Dr. Beckett to revert Wraiths to human form puts Sheppard's life in jeopardy after the team encounters a girl in the early stages of Wraith development. Ellia: Jewel Staite.

Beckett and McKay race to curb Sheppard's disturbing metamorphosis when he begins to exhibit Wraith traits after being exposed to a strange virus.

The Atlantis team crosses paths with the Aurora, a massive vessel ferrying a surprise set of passengers---Ancients. Captain: Bruce Dawson. First Officer: Pascale Hutton. Crewman: Ryan W. Smith.

Part 1 of two. Sheppard and his team catch up with the erratic Lt. Ford, who enlists their help for his attack on a Wraith hive ship---a plan Sheppard equates with suicide. Unfortunately, the effects of the Wraith enzyme have made Ford immune to reason. Kanayo: Aaron Abrams. Jace: Paul Anthony.