24 (season 4)  The fourth season of the American drama television series "24", also known as Day 4, premiered on January 9, 2005, on Fox and aired its season finale on May 23, 2005. The season four storyline starts and ends at 7:00 am. The fourth season is set 18 months after season three. Jack is now working for Secretary of Defense James Heller after being fired by CTU due to his heroin addiction. As the day begins, he gets caught up in an elaborate terrorist plot which involves James Heller and his daughter Audrey Raines. Unlike previous seasons as well as later ones, which focus on a singular threat, multiple enemies, and conspiracies, this season is based around one main enemy: a terrorist named Habib Marwan who controls a series of Middle Eastern terrorist cells that launch attacks against the United States. Rather than large acts, this season is divided into several smaller acts depending on which terrorist threat Marwan is focusing. Day 4 begins with the bombing of a commuter train which (unbeknownst to CTU at the time) enables the theft of a device known as the Dobsen-type Override which could be used to take control of (and melt down) United States nuclear power plants. With Jack Bauer working for Secretary of Defense James Heller, his job brings him to CTU as a visitor on this very day. Believing that something terrible is about to happen, Jack begs CTU director Erin Driscoll to reinstate him and begins to interrogate a suspect. The suspect reveals that James Heller and Audrey Raines are the primary targets just as they are kidnapped. When Jack saves a civilian programmer who discovered evidence of a cyber-attack in progress (a friend of Chloe O'Brian), he allows one of the terrorists to escape and lead him to where Raines and Heller are being held. Even though Jack rescues them, the mass streaming of the planned execution video gives the terrorists the opportunity they need to launch an attack on the firewalls and begin using the override. CTU finds out about the override with the help of Bauer and Tony Almeida and identifies the man responsible for using it: Habib Marwan, an employee of the defense contractor that developed the override. Marwan is able to sabotage one plant, the San Gabriel Island reactor, before Jack's team puts him on the run. Seeking extra intelligence, Bauer and Paul Raines (Audrey's ex-husband) travel to the headquarters of the defense contractor McLennan-Forrester.