This is the closing episode to the replicator story line. or is it?
The replicators made ti to Earth and have invaded a Russian sub. it's up to the team to find a way to stop the little buggers before they devour everything in their path.
The Asgard take Sam to one of their worlds in hopes that she is "Dumb" enough to come up with a simple way of defeating the Replicators. Basically the Asgard always over think the situation. They also reveal they have a massive state of the art battleship called the "O'Neill", Which she uses to lure the Replicators to their doom while Jack and Teal'c lead a team to the sub in order to defeat the invading force.