Season 2 takes place 18 months after Season 1.
Jack leaves CTU and isolates himself, so George Mason becomes the Director of CTU LA.
Kim leaves and recently becomes a live-in nanny for the Mathison's.
David Palmer has won the election and is now President.
It has been discovered that a terrorist group has a nuclear bomb and is planning to detonate it in LA. The terrorist group is Second Wave and there was one federal agent that had previously worked undercover to bring down the group - Jack Bauer.