24 Episodes · Premiered October 28, 2003 · Ended May 25, 2004
Is set three years after Season 2 ends. It begins at 1:00 p.m. Jack must again infiltrate a Mexican drug cartel to seize a deadly virus being marketed underground. Meanwhile, Palmer attempts to be devoid of further political scandal which could cost him his presidency. Later, Jack and Palmer must cooperate with terrorist Stephen Saunders, who eventually gains possession of the virus, and stop him from releasing it in several American cities.
Jack witnesses a murder linked to his lengthy undercover assignment; the delivery of a contaminated corpse precedes a threatening call to the FBI. Chase.
Jack and Chase visit the last address of the infected body; Palmer suggests cancelling the debate, but Wayne disagrees, hinting at a vulnerability in their opponent; Hector's location is narrowed down.
Kyle's parents get a clue about his activities; Wayne finds a solution to the problem regarding Anne; Salazar requests another meeting with Annicon; the virus's infection and fatality rates are revised upward.
CTU receives instructions for Salazar's delivery; Kyle and Linda get a glimpse of what they're into; Chase disobeys Jack, who makes a report, and a suggestion, to the president.
Jack's diversion at the prison comes back to bite him; Gael seeks to slow CTU's tracking of Kyle; Kim is rattled by news of Jack's activities; Keeler plays the Anne card at the debate.
After Chappelle takes command at CTU, Chase lobbies him to get Palmer's input on Jack's situation; Kim's emotional state is questioned; Kyle's parents get a prognosis on their son.
Michelle asks Gael to take over for her; Chase gets help in disobeying Chappelle to pursue a lead on Jack's location, where Ramon grows impatient; Anne is contacted by her ex-spouse.
Wayne and the president disagree over Jack's actions, which are explained to Ramon; CTU tries to intercept Chase; Anne gets more than she wants from her ex-husband.
Michael changes the arrangements for the sale; Jack gets an ally; Palmer is summoned by an important supporter; Tony's competence is questioned.
Gael speaks to Jack; Wayne tries his own field op when Milliken flexes his muscle against Palmer; Sergio delivers disturbing news to Hector; Chloe responds to a family emergency.
Emotions carry weight as Palmer makes a deal in his "street fight" with Milliken; Hector's doubts about continuing the operation cause dissension with Ramon; Kim gets a disturbing assignment.
Tensions escalate at CTU with the arrival of a cocky systems analyst and a question about Chloe's baby; Sherry gets the goods on Milliken, but Palmer balks at the price.
Nina takes things in a new direction, and adds a new player; Chloe is out of service when CTU needs her most; Sherry launches a stealth op against Milliken.
Sherry lies to Palmer about seeing Julia; Alvers alters the virus; Nina is introduced to new interrogation techniques, while Jack is also questioned regarding his past infiltration of the Salazars.
CTU IDs the system likely to launch the virus; Amador is chastised by his employer, who's familiar with Jack; the police question Julia without a lawyer present.
Extreme force is ordered to isolate the hotel; Sherry threatens Palmer over Milliken's death; the amount of virus remaining and its altered power is determined; a conspirator makes a deal to tell what he knows.
The link is found between Jack and Saunders, who makes his first demand of Palmer; Jack uses a legal loophole against a new witness; Michelle lobbies to ease the pain of the infected.
Jack prepares Chappelle for his assignment; a hotel guest reports a missing companion who may have left the hotel with the virus; Michelle gives the infected the cold truth, with an option.
Jack urges caution with a new lead and it comes back to bite him; Cole seeks help for his nose; Palmer convenes the cabinet before hearing Saunders' next demand, and ultimate goal.
The president is ordered to leave L.A., and asks the press to help maximize public safety; Jack gives Jane a crash course on her father; the virus affects another CTU operative.
As Saunders keeps him on a tight rein, Tony scurries to cover his tracks, while the rest of CTU suspects another mole; Sherry Palmer makes an offer of assistance.
Michelle tries to unnerve one of her captors; Keeler personally plays his card against Palmer; Tony argues with Saunders over arrangements for their trade.
Jack argues for Tony, who's taken into custody; an implacable Saunders tells the time of the next attacks; Wayne and Foxton have differences on their operation as time runs out, and afterward.
Saunders reveals the B-plan of the last courier, who benefits from a CTU snafu that gives Tony a temporary reprieve as he's called back to the case. Meanwhile, Chase makes decisions about his future.
