Confident that the destruction of Thor's starship has ended the Replicator threat to Earth ("Nemesis"), the SG-1 team returns home through the second Stargate that has been put up at Stargate Command. Shortly after they learn that a Russian Foxtrot class submarine has been hijacked by creatures whose descriptions match the Replicators, Thor arrives at Stargate Command and asks SG-1 for help against the Replicators in the Asgard galaxy. As Colonel O'Neill (Richard Dean Anderson), Daniel Jackson (Michael Shanks) and Teal'c (Christopher Judge) go to deal with the hijacked submarine, Major Carter (Amanda Tapping) goes with Thor.