Carter and Teal'c go in search of the Asgard to try and save Colonel O'Neill, but discover that the Asgard's enemy has returned with a vengeance. The System Lords seek an alliance with Earth against a common enemy.

While the Goa'uld threaten to attack Earth, SG-1 and the Asgard make a last, desperate stand against the Replicators, which have captured Major Carter and invaded the last outpost of the Asgard civilization.

When SG-1 finds a vital clue in its search for the Lost City of the Ancients, Dr Weir prepares her team for a perilous journey under the sea.

Unable to return to Earth, the crew looks for a new fuel source. They happen upon a settlement, but the villagers live in fear, the enemy is coming.

The S.G.C. is put under quarantine after a mysterious infection leaves a Russian officer in the infirmary but the disease may not be a disease at all.

The Atlantis base is threatened when the team discovers that an alien entity is in the city. McKay grows worried when he is unable to remove an Ancient shield device.

General O'Neill tries to settle into his new job, but faces never-ending crises, including the capture of SG-1 by the Goa'uld.

The team finds themselves in mortal danger when their Puddle Jumper ship becomes lodged in the Stargate.

Daniel is stranded on another planet after the team's arrival on an alien world sparks a violent civil war.

After a series of run-ins with the Wraith, the team begins to suspect their Athosian allies of having a spy in their midst.

Teal'c is trapped in a virtual reality simulation, in which he must defend the base from a Goa'uld super-soldier incursion.

Sheppard and the team visit a world where no one is over 24 years old because of a ritual suicide practice they believe keeps the Wraith at bay.

Teal'c becomes the chief suspect in a murder investigation after he moves into an apartment off-base. Carter considers her future with Pete.

The team finds a world whose people are on the brink of a discovery that may make them immune to the Wraith feeding.

A businessman threatens to expose the secrets of alien life to the world, forcing Stargate Command to bring him into the loop.

Efforts to open trade relations with a species called the Genii turn sour when the team discovers their new "allies" have ulterior motives.

The impending wedding of his son is the least of Teal'c's worries when the Hak'tyl plan an uprising against the Goa'uld Moloc, driving a wedge between Teal'c and Ishta.

McKay's efforts to harness the energy of an alien planet's atmosphere allows for a return trip to Earth but the team may not be able to return to Atlantis.

The Stargate is stolen, leading SG-1 to discover that the Trust has taken control of an advanced ship in orbit. Teal'c investigates a series of wide-spread Jaffa deaths.

A duplicate of Colonel Carter seeks help from Stargate Command in defeating the Replicator Fifth, who she claims has found a way to counter the Asgard's new weapon.

When a massive storm threatens the city, Atlantis is evacuated only to be taken over by the team's newest enemy.

Major Sheppard plays a dangerous game of cat and mouse with soldiers who have seized control of Atlantis and taken Weir and McKay hostage.

After the Prometheus responds to a distress call from a Goa'uld ship, Daniel Jackson finds himself a captive when Earth's ship is stolen.

Sheppard's team investigates a downed Wraith ship, and find themselves stuck on a planet with a lone Wraith survivor.

SG-1 comes to the aid of a world about to be invaded by the Goa'uld, only to discover that the local king is Earth's Harry Maybourne.

Nearly a third of Atlantis's residents are infected with a deadly virus that causes hallucinations and death, forcing a lockdown of the city.

Relations between the U.S. and Russia are strained when Russian military leaders claim that the U.S. government has been compromised by the Goa'uld.

The team finds a paradise world that would make an ideal sanctuary for those fleeing from the Wraith, but the local inhabitants believe their goddess will not permit it.

A barber from Indiana confronts Jack O'Neill, claiming that he has been seeing visions of SG-1's missions over the last seven years.

A woman is found in suspended animation in Atlantis, and the team is shocked to see that it is Dr. Weir herself, who tells them of her trip 10,000 years into the city's past.

The Replicators begin a systematic attack of the Goa'uld, forcing Baal to come to Earth for help. The Jaffa resistance risk their entire movement in an attempt to retake a holy city in Baal's domain.

The fate of the galaxy hangs in the balance as Sam and Jacob search for the only weapon capable of stopping the Replicator onslaught. O'Neill leads a defense of the S.G.C., while Daniel squares off against Replicator Carter.

Daniel must once again decide whether to risk death or ascend when Oma Desala gives him a second chance. O'Neill and Carter struggle with their respective personal relationships.

The team searches for a valuable Zero Point Module rumored to be hidden on the planet Dagan but their new allies have motives of their own.

With a brief opportunity to send a data transmission to Earth, members of the Atlantis expedition compose video messages home to their loved ones.

Plagued by terrifying nightmares, Teyla begins to recall a time when she and her father were captured by the Wraith and subjected to disturbing experiments.

SG-1 travels back in time in a daring plan to steal a piece of Ancient technology from Ra, the powerful Goa'uld who ruled in ancient Egypt.

With the timeline changed by SG-1's actions in the distant past, an alternate version of SG-1 must use the newly-discovered time ship to set things right.

With a group of Wraith hive ships on the way to Atlantis, the team searches for a place to flee and a way to destroy the city. McKay leads a team to try and activate the Ancients' orbital weapons platform.

A new military contingent from Earth is sent to take command of Atlantis and defend it from the impending Wraith attack.