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.

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.

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.

Samantha Carter returns to Stargate Command when the Ori seize control of a planet, using an expanding force field to gain a foothold in our galaxy.

SG-1 investigates when evidence suggests that there are still Goa'uld hiding on Earth -- including a former System Lord. Tensions between Earth and the Free Jaffa continue to mount.

Daniel is imprisoned on a world under the influence of the Ori, and the Prometheus is caught in a firefight when SG-1 tries to rescue him.