The Daedalus arrives to defend Atlantis from the Wraith onslaught, but it may not be enough when the team discovers that an even larger armada is on the way.

The Daedalus is infected by a Wraith computer virus, while members of the expedition hope to return to Earth.

The team desperately attempts to stop two Wraith hive ships from reaching Earth. Sheppard must rely on an old foe to rescue McKay and Ronon.

As a mysterious new illness sweeps through the Pegasus Galaxy, Teyla is convinced by a vision that the father of her child is trying to communicate with her.

Sheppard returns to Atlantis after a mission and finds the city abandoned, all systems dead -- and instead of ocean, sand dunes as far as the eye can see.