Series 1: The first episode begins at midnight on the day of the California Presidential Primary. Jack Bauer (Kiefer Sutherland) heads up the government's Counter-Terrorist Unit. He discovers that there's going to be an assassination attempt on Senator Palmer (Dennis Haysbert), an African-American presidential candidate. Bauer faces a battle against the clock to avert disaster.

The series follows several characters as they live through a day that none of them will forget. For Kimberly (Elisha Cuthbert) a night on the town takes an unexpected turn. Teri (Leslie Hope) sets out to find Kimberly and encounters more danger than she ever imagined possible. Senator Palmer, unaware there's going to be an attempt on his life, faces the threat of a long buried scandal resurfacing. Meanwhile, Jack, with help from his Chief-of-Staff Nina Myers (Sarah Clarke), is charged with the responsibility of stopping the assassination. But who can he trust when it appears a rogue element inside the Agency is in on the hit?

And all the time, the clock keeps ticking...

Series 2: Jack Bauer (Kiefer Sutherland) and the Counter Terrorist Unit (CTU) race to prevent a nuclear bomb being detonated by terrorists in Los Angeles in the second season of 24.

Series 3: When the head of a Mexican drug cartel is imprisoned by Jack Bauer (Sutherland), a plot ensues to blackmail the US Government with the threat of a released bio-weapon that will kill millions to ensure his release. With Palmer seeking re-election to a second term, will Jack survive this day?

Series 4: 18 months after day 3, CTU has a new leader, Erin Driscoll, a steely government agent who made firing Jack one of her first priorities. After the explosion of a commuter train, Jack, who is now working for Secretary of Defense James Heller and also is romantically involved with Heller's married daughter, Audrey Raines, suddenly finds himself heading back to CTU for a meeting with Driscoll. Jack believes that the train explosion is a prelude for bigger things to come...

Series 5: 18 months have passed since the events of Day 4. With the exception of David Palmer, Tony Almeida, Michelle Dessler and Chloe O'Brian, the world believes that Jack Bauer (Kiefer Sutherland) is dead...

Jack is, in fact, living under the name of Frank Flynn and conceals his identity by taking a manual job on an oil rig. However, when President Logan is placed at the centre of a labyrinthine conspiracy involving the signing of a vital U.S. - Russian arms treaty, Jack is forced back into action!