Season 4 begins as Dr. Weir clings to life and Dr. McKay tries to save Atlantis, which is badly damaged and lost in space after the Replicator attack. Amanda Tapping joins the cast. Jewel Staite.

McKay and Sheppard prepare to steal a ZPM from the Replicator home world; Col. Samantha Carter links up with the Apollo to search for Atlantis. Jewel Staite. David Ogden Stiers.

A mission against the Wraith has the Atlantis team collaborating with a group of Satedans from Ronon's past. Christopher Judge.

While exploring a jungle planet, Lt. Col. Sheppard comes into contact with a crystalline growth that turns him into a host for an infectious alien life form.

On a return flight to Atlantis, a jumper is seized and its pilot, Lt. Col. Sheppard, is taken prisoner by Larrin (Jill Wagner), the commander of a rogue human ship.

The crew suffers from amnesia after plant samples from their new home planet unleash a virus that affects everyone except Teyla and Ronon. Kavan Smith, Zach Selwyn.

Teyla and Dr. Keller uncover a mystery on New Athos, where they find an abandoned Athosian settlement and a hostile warrior tribe. Nabel: Johann Helf. Omal: Danny Trejo.

Atlantis receives a visitor with psychic abilities, who delivers a dark forecast about the outpost. Richard Woolsey: Robert Picardo. Martin Jarvis, Kimberley Warnat.

Jeanie Miller (Kate Hewlett), Dr. Rodney McKay's sister, is kidnapped on Earth, prompting a response from the Atlantis team. Henry Wallace: Steven Culp. Agent Malcolm Barrett: Peter Flemming.

A strange drone crashes into Atlantis, heralding a dreadful new predicament.