Having regained control of the X-303, the SG-1 team finds itself in an unknown part of space. Rescue comes in the form of the Asgard, specifically Thor, who needs their help. The Asgard home world has been overrun by the Replicators and they require SG-1's help as well as the relatively low tech X-303. The Asgard had set a trap for the Replicators and hoped to use a time dilation device that would give them the time they need to find a way to defeat them. The problem is that the Replicators have turned off the device and the Asgard want SG-1 to go in and activate it. They accept the assignment but to meet their objective, O'Neill will face a moral dilemma.

When an SG geological exploration mission runs into deadly conflict with an indigenous Unas clan, Daniel gets Chaka to help seek an accord with it.

In exchange for new tech for the SGC, Warrick Finn asks for their help to win a dangerous spaceship competition.

In a last ditch effort, O'Neill activated an Ancient weapon in the Antarctic to defeat Anubis. With Jack still in stasis in the Ancient outpost buried in Antarctica, SG-1 tries to contact the Asgard. Meanwhile their new leader, Dr. Elizabeth Weir, tries to decide what to do about a request for peace talks from the Goa'uld System Lords.

The Asgard fleet has managed to destroy the Replicator ship, with Carter aboard, but cannot contain the debris. Talks break down with the System Lords, ending in a Ha'tak being dispatched to test Earth's new defensive capabilities. The Prometheus waits to engage the incoming enemy, but Thor arrives in the Daniel Jackson, with Teal'c aboard. They enlist the help of Daniel and Jack, still in stasis, to remove the threat of the replicators to the new Asgard homeworld.

The replicator Carter and the real Carter work together with the disruptor signal. The replicator has a different plan.