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. Season overview 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 other seasons 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. A train bombing is a diversion to kidnap the secretary of defense and his daughter. A device from the train is used to initiate the forced meltdowns of nuclear power plants across America. Terrorists steal a stealth fighter to shoot down Air Force One. The terrorists steal the nuclear football, allowing them to launch a nuclear missile towards Los Angeles that must be intercepted. Major subplots When Jack Bauer returns to field work, he clashes with other members of CTU over how operations should be run. Jack's relationship with Audrey is strained because she is horrified at the pain he is willing to inflict to acquire information. Audrey's brother Richard withholds information that could help CTU by claiming they have no right to invade his privacy. The Araz family is torn apart by conflicting opinions about the morality of inciting a nuclear catastrophe. Curtis suspects a co-worker, with whom he was previously involved, of being a mole. The crisis prevents Erin Driscoll, the new director of CTU, from being able to look after her daughter who has schizophrenia. Tony Almeida and Michelle Dessler although divorced, find themselves working in the same office again. Charles Logan feels overwhelmed when he unexpectedly takes over the presidency during a crisis. David Palmer begins to discover corruption within the government. After the Chinese consul dies of friendly fire, CTU attempts to cover up the fact that Jack Bauer invaded the Chinese consulate. Summary Day 4 begins with