Doctors discover a Goa'uld larva has attached itself to Kawalsky's (Jay Acovone) brain; Carter is kidnapped on a planet by the son of the local chief; and an infection causes its victims to become animalistic brutes.
Earth is threatened with destruction; Carter's body is taken over by a parasitic alien; and O'Neil and his team are banished to a penal world.
O'Neill is implanted with a Goa'uld symbiont; he falls victim to a biological agent used by the leader of a cult to brainwash his followers; and enters into negotiations with the Goa'uld in a bid to decide Earth's future.
Replicator bugs multiply aboard a submarine; the team embarks on a mission of mercy in response to a plea from the inhabitants of Euronda; and the team are supplied with power-enhancing armbands.
The team fights for survival against Apophis; Teal'c undergoes a dangerous ritual to free his brainwashed mind; and Carter wakes from a blackout to find she has acquired a new friend.
Teal'c returns home to attend his wife's funeral; team members accidentally activate the self-destruct mechanism on a Goa'uld mothership; and O'Neill contracts a deadly virus from a woman who has been frozen in ice.
Jackson helps the team trap the Goa'uld system lord Anubis; Anubis prepares to attack Kelowna and steal the Naquadria; and a teenage boy turns up claiming to be O'Neill.
Carter and Teal'c try to find the Asgard in a bid to cure O'Neill; the Stargate Command is put under quarantine; and O'Neill settles into his new job as commander of the base.
New arrival Lt Col Cameron Mitchell (Ben Browder) tries to reunite the original members of SG-1; a group of gods threatens to destroy Earth; and Jackson and Vala (Claudia Black) take part in a series of missions to unlock the Jaffa device.
Vala's rapidly aged daughter Adria (Morena Baccarin) is proclaimed the new leader of the Ori; Landry (Beau Bridges) finds it difficult to trust Vala; and Carter and Mitchell join forces with Dr McKay (David Hewlett) to shut down the Ori supergate.