

With changes in leadership and new allies, the team continues to battle the Wraith and confront new existential threats. Personal dynamics shift as members struggle with loss and make significant choices that shape the fate of Atlantis and its mission in the Pegasus Galaxy.
All episodes — Season 4
S4 E1Adrift (2)
Sep 27, 20078.244 min
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.
S4 E2Lifeline (3)
Oct 4, 20078.443 min
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.
S4 E3Reunion
Oct 11, 20077.644 min
When a group of Ronon's people enlist the team's help in raiding a Wraith weapons facility, Ronon reconsiders whether his future lies in Atlantis or with his friends.
S4 E4Doppelganger
Oct 18, 20077.343 min
During an off-world mission Colonel Sheppard unknowingly becomes host to an alien entity, which infects others in Atlantis and afflicts them with terrifying nightmares.
S4 E5Travelers
Oct 25, 20077.643 min
Colonel Sheppard is captured by the inhabitants of a generational ship and their beautiful leader, who wish to use his ability to use Ancient technology for their own ends.
S4 E6Tabula Rasa
Nov 1, 20078.144 min
When a virus causes amnesia in everyone except Teyla and Ronon, the Atlantis team must work together to find a cure before their memories fade entirely.
S4 E7Missing
Nov 8, 20077.144 min
During a visit to New Athos, Teyla and Dr. Keller find themselves on the run from a primitive tribe of warriors.
S4 E8The Seer
Nov 15, 20077.544 min
The team meets a man with extraordinary prophetic abilities, who gives them a dark prediction about Atlantis's future. The Wraith seek a new alliance with Atlantis in their war with the Replicators.
S4 E9Miller's Crossing
Nov 29, 20077.644 min
Rodney McKay goes in search of his sister on Earth after she is kidnapped by the head of a powerful corporation.
S4 E10This Mortal Coil (1)
Dec 6, 20077.944 min
A mysterious drone crashes into Atlantis, indicating that the Replicators may have found the city. But when Elizabeth Weir appears, the team realizes that the probe is just a part of a bigger mystery.
S4 E11Be All My Sins Remember'd (2)
Jan 3, 20088.544 min
With a plan to potentially extinguish the Replicator threat, the Atlantis team must seek an alliance with a fleet of Wraith ships.
S4 E12Spoils of War
Jan 10, 20087.644 min
The team finds their former Wraith ally's hive ship drifting in space, which leads them to a secret project that could turn the tide of a civil war.
S4 E13Quarantine
Jan 17, 20087.544 min
An automated lockdown traps Atlantis personnel in various parts of the city, each of them hoping the others will come to their rescue.
S4 E14Harmony
Jan 24, 20086.844 min
Colonel Sheppard and Dr. McKay must protect a child princess on a pilgrimage before she can become queen, and learn that she has dangerous enemies threatening her life.
S4 E15Outcast
Jan 31, 20087.243 min
While on personal leave on Earth, Sheppard and Ronon learn that scientists have engineered a human-form Replicator -- who is now on the loose.
S4 E16Trio
Feb 7, 20087.644 min
McKay, Carter, and Keller are trapped in an underground chamber while on an off-world mission, with no apparent means of escape.
S4 E17Midway
Feb 14, 20088.244 min
Teal'c visits Atlantis to counsel a headstrong Ronon, who is up for review by the I.O.A. But the two must work together when the Wraith invade the Midway space station in order to reach Earth.
S4 E18The Kindred (1)
Feb 21, 20087.844 min
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.
S4 E19The Kindred (2)
Feb 28, 2008844 min
The team is shocked when an old friend, believed to be dead, miraculously returns to them. Teyla plans an escape from Michael's captivity.
S4 E20The Last Man (1)
Mar 6, 20088.544 min
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.