Combat engineers from Atlantis work against the clock to rescue four of their colleagues who are now trapped in the rubble of Michael's medical compound. With Michael en route, they quickly locate McKay and Major Lorne but Sheppard and Ronon are far deeper and their rescue is not assured. When Michael's ship arrives, they decide to try to rescue Teyla who is in labor and close to giving birth. When it's all over, Col. Carter is recalled to Earth for a performance review but Richard Woolsey has some bad news for her.

Dr. Carson Beckett is removed from stasis because he's the only one who can find the antidote to a mysterious virus that has incapacitated base personnel, beginning with Dr. Jennifer Keller.

Ronon is abducted by a Wraith who tries to brainwash him.

An empty Daedalus is found orbiting the planet. The team goes to check it out and they are transported to an alternate universe.

When the power is shut down and most of the inhabitants are locked out of key controls, it is apparent that Atlantis has been taken over by an off-world group, soon identified as Michael and his hybrids. He is after Teyla's newborn child who is key in his quest to gain control of the Pegasus galaxy. While Sheppard and McKay try to get their hands on a jumper to launch an attack, Ronon and others who were taken prisoner by Michael during his initial invasion launch reprisals of their own. When Teyla manages to get away and hide, Michael gives her a simple choice: surrender herself and her child to him or he will use the city's self-destruct mechanism to kill everyone.