An unstoppable energy weapon leaves Atlantis under siege after Earth launches a preemptive attack against a very powerful enemy's homeworld.

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.

With a plan to potentially extinguish the Replicator threat, the Atlantis team must seek an alliance with a fleet of Wraith ships.

"Todd" informs the Atlantis expedition that a rogue group of Wraith has acquired several Zero Point Modules to power a Super-hive, and wants it destroyed. However, after the Daedalus is disabled, they learn that the ship is heading straight for Earth, and they must stop it before it gets there.