Counter-terrorism agent Jack Bauer attempts to stop the assassination of United States Senator David Palmer on the day of the California presidential primary, while those spearheading the assassination plot stop at nothing to exact revenge on Bauer and Palmer.

The second season is set 18 months after season one. The season's main plot follows the work of now-U.S. President David Palmer and agent Jack Bauer to stop terrorists from detonating a nuclear bomb in Los Angeles. Introduced into the situation is Kate Warner, a woman who ends up getting vital information related to CTU's mission.