24 - Season 4 (DVD)

18 months after Day 3, CTU has a new leader, Erin Driscoll (Alberta Watson), a steely government agent who made firing Jack Bauer (Kiefer Sutherland), one of her first priorities on taking up command. After the explosion of a commuter train, Jack, who is now working for Secretary of Defence James Heller (William Devane), and who is also romantically involved with Heller's married daughter, Audrey Raines (Kim Raver), suddenly finds himself heading back to CTU for a meeting with Driscoll.

Jack believes that the train explosion is a prelude to bigger things to come, and when it seems as if Islamic terrorists are launching an all out assault on the USA, Jack is called back to lead CTU's response.