Curtis brings in a suspect who has critical information about Marwan's next strike. Michelle orders Curtis to use harsh methods to interrogate the suspect, but things get complicated when Marwan sends a lawyer to defend his rights. Logan's advisors begin to worry as he continues to exhibit fear in the face of the ongoing terrorist threat.

The episode was rated 7.99 from 410 votes.

Marwan decides to trade Jack for Behrooz in hopes of distracting CTU from his real objective. Tony and Michelle weigh the consequences of the trade, while Curtis reluctantly interrogates Behrooz in order to learn more about Marwan.

The episode was rated 7.99 from 410 votes.

Jack takes Audrey to ID the man she recognized at the compound, but the terrorists get there soon after and pin them down. Jack must call on an old friend to help him escape. Heller puts Edgar in charge of dealing with the nuclear override, while Driscoll's daughter takes a turn for the worse. Dina is wounded when she helps Behrooz flee from Navi. Navi's boss orders him to kill his wife and son before the day is over.

The episode was rated 8.00 from 424 votes.

Jack and Curtis finally learn the location of the override device. They try to trap the architect of the terrorist strike before the remaining nuclear plants go critical. Tony pushes Dina to reveal more of her knowledge of Marwan, while Driscoll faces another personal crisis with her daughter.

The episode was rated 8.00 from 413 votes.

Eighteen months have elapsed since the conclusion of Day 3. A commuter train bound for Los Angeles explodes. A man steals a suitcase from a passenger in the wreckage and then kills him. Jack has been dismissed from CTU and now works for Secretary of Defense James Heller. Jack is involved with Heller's daughter, Audrey, and their relationship is growing serious. Jack is in LA for a meeting with CTU Director Erin Driscoll, who fired him a year ago, but he finds himself alienated at CTU by Driscoll and the new staff when reports of a possible terrorist strike come in. A young computer hacker named Andrew Paige sees something that he shouldn't on the Internet. Suddenly, he finds himself running for his life as he is pursued by terrorists. Luckily, he is able to warn Chloe O'Brian before its too late. The Turkish Araz family are not what they seem and it becomes clear that they are heavily involved with the day's events. Meanwhile, Heller has a confrontation with his estranged son. Jack finds that Chloe is his only ally as he tries to prove that the train explosion is merely a diversionary target.

The episode was rated 8.02 from 507 votes.

Jack and Paul enlist civilian help when they must fight off soldiers sent to kill them by McLennan-Forster. Tensions flair between Tony and Michelle as she assumes command of CTU. Sarah tests Michelle's authority by giving her an ultimatum. Audrey reevaluates her feelings for Jack, while Marwan sets the next phase of his plan in motion.

The episode was rated 8.02 from 408 votes.

Jack and Paul visit the defense contractor who employed Marwan, but the company executives put their own interests ahead of CTU's and take major steps to destroy evidence. After a grief-stricken Driscoll relinquishes her command, Heller appoints Tony as interim director to oversee the latest crisis.

The episode was rated 8.03 from 423 votes.

Jack and Audrey hide out with an embittered Tony as Audrey makes a positive ID of the man from the kidnapping. Marianne successfully diverts suspicion from herself, leading Driscoll to torture the wrong person for information. Behrooz takes Dina to a hospital for medical attention, but the doctor becomes suspicious of her gunshot wound and phones the police.

The episode was rated 8.04 from 430 votes.

Mike pushes for the Vice-President to be sworn into office as the White House waits for news of Keeler's fate. Two innocent bystanders are dragged into the fight as Jack and Marwan both pursue a briefcase that contains the launch codes for America's nuclear arsenal.

The episode was rated 8.05 from 396 votes.

CTU scrambles to forge an alibi when a Chinese representative produces evidence of American involvement in the raid on their embassy. Audrey gives Jack the cold shoulder, while Palmer and Logan clash over the consequences of Palmer's decisions. Jack and Curtis close in on Marwan as the countdown for the missile launch moves ahead.

The episode was rated 8.06 from 392 votes.

Mandy uses Tony as leverage to try to force Michelle to aid in her escape. A Chinese security operative captures and interrogates one of the CTU agents involved in the raid on the embassy. Palmer and Logan argue over the option of evacuating all major cities that may be targets for the missile.

The episode was rated 8.09 from 397 votes.

After Logan authorizes Palmer to take charge of the crisis, Palmer sanctions Jack and Curtis to infiltrate the Chinese Embassy on a covert operation to capture a suspect. Tony and Michelle continue to bump into each other's personal lives, while Buchanan expresses anger at being kept out of the mission. Jack faces Audrey's wrath when a medical dilemma places Paul's life in jeopardy.

The episode was rated 8.11 from 392 votes.

CTU raids Marwan's hideout, but he manages to slip through their fingers. Luckily, Jack locates a lead that may help him identify Marwan's next target. Tony becomes suspicious of Michelle's personal life, while Audrey reunites with Paul and learns the extent of his injuries. Anderson closes in on his quarry, as President Keeler searches for words that will comfort the American public.

The episode was rated 8.14 from 418 votes.

Chloe is unexpectedly thrust into fieldwork when a woman reports that her boyfriend may be part of the terrorist conspiracy. Jack and Curtis find their latest efforts to trap Marwan thwarted by the Secret Service, who have orders to arrest Jack for insubordination. Mike calls on ex-President David Palmer for help as Logan continues to display a lack of leadership.

The episode was rated 8.20 from 412 votes.

As the missile speeds toward its destination, Mandy cuts a deal with Jack and the President to give up Marwan's location in exchange for a full pardon on all of her crimes. Tony and Michelle share a happy reunion, but Jack finds his relationship with Audrey shattered as she makes her feelings known. Logan's advisor suggests a drastic course of action when the Chinese government demands that Jack be handed over to them for trial. Palmer tries desperately to warn Jack of the danger against him. Jack's life changes forever as Tony, Michelle and Chloe help him to evade the trap set for him by Secret Service.

The episode was rated 8.36 from 388 votes.