Jack tries to undermine Eddie's mission to bomb CTU while George investigates intel leading him to the site of the nuclear bomb's construction and Kim tries to make contact with her father by heading for CTU headquarters.

George returns to CTU where he orders the medics to revive a badly injured Paula, who has vital information. Palmer comes down hard on Eric for his deception. Kim takes Megan to the hospital, but the staff accuses her of abuse. Jack locates the leader of the American terrorist cell. He learns that the woman who gave them inside information on CTU is an old enemy.

George refuses to allow Jack to assist in Nina's interrogation. Jack resorts to blackmail to change George's mind. Palmer and Stanton meet with a Middle Eastern ambassador who may be in league with Second Wave. Tony visits the Warner home and questions Reza about his possible connection with Syed Ali.

Jack begins his interrogation of Nina and pushes all boundaries in order to force her to divulge the name of her contact. Palmer is surprised and suspicious when his ex wife Sherry returns and claims to have information about a conspiracy against him from within his own administration. Kim and Miguel plan to kidnap Megan from the hospital in order to take her out of LA and away from the nuclear threat.

Jack forces Nina to help with a sting operation against her contact in the hopes that he can lead them to the bomb. Palmer and Mike try to gage Stanton's loyalty when they investigate the chopper crash. George has a final conversation with his son.

Kim and Miguel are arrested and the police plan to take them back to LA. Tony questions Bob Warner at CTU and learns more about his government connections. Palmer discovers a traitor in his ranks when the journalist whom he was holding is set free. Nina pulls a deadly countermove, setting herself up as the main player in the search to locate the bomb.

George pits Bob against Reza in hopes of learning which one is working with Second Wave. Sherry and Lynne clash over Palmer's speech to the press. Kate is interrogated by Syed Ali, who believes she knows too much about the bomb. Jack and Nina fight off a group of renegade soldiers while waiting to be rescued from the crash site. They nearly escape when Nina takes Jack hostage and demands to speak to the President.

Two traitors are uncovered. One is the mole in the Palmer administration who is working with Stanton. The other is the member of the Warner family who helped Syed Ali to bring the bomb into the country. Jack learns of Ali's location and tries to rescue Kate. Kim and Miguel hatch an escape plan to stay out of LA, but the results are disastrous.

Kate helps Jack to locate and identify Syed Ali. Palmer places Stanton under arrest, but he won't break. Palmer realizes he must go to extremes to make Stanton talk. Kim hits her low point of the day when she encounters a cougar in the woods.

Jack engages in a brutal contest of wills with Syed Ali. George questions Bob Warner to learn more about Marie's motivations for helping the terrorists. Kim is rescued by a mysterious hunter who offers her asylum. Lynne receives a dire warning from Sherry.

Jack and his men prepare for a confrontation with Stanton's renegade soldiers as they converge on the bomb. Kim becomes suspicious of her host, but is forced to stay because of her status with the police. Stanton finally breaks down and gives Palmer some unpleasant news.

Jack and Kate try to break Marie's resolve so they can learn the location of the bomb. Palmer confronts his ex wife with the information that Stanton gave them. George finally steps down as director of CTU and hands the position over to Tony. Kim discovers her host's deception.

Palmer, Mike and Lynne discuss various ways to dispose of the ticking bomb. They conclude that the desert is the best place to set it off. Jack determines that one man must pilot the plane carrying the bomb. He chooses to fly the plane himself and bids a tearful goodbye to his daughter. Tony and Michelle become suspicious of a Middle Eastern diplomat who is asking questions about the evidence against Syed Ali. Palmer departs for Los Angeles so he can be on hand when news of the nuclear bomb reaches the public.

Jack and Michelle question Syed Ali, who claims that the audio recordings are false. Palmer prepares to wage war against the three countries who were involved in the nuclear strike. Kim gets caught in a hostage situation. Jack is contacted by a man who wants to exchange information for Kate Warner.

Three years have passed since the events of Day Two. A van deposits a dead body outside the LA Health Unit. The body is infected with a deadly virus. Tony, now in charge of CTU, learns that this is a blackmail tactic to get the US government to release a drug lord, Ramon Salazar, whom Jack has just brought down, before Salazar's brother releases the virus into LA.

Jack and his new partner, Chase Edmunds, prepare to sign a deal with Salazar at the prison. Salazar delivers a mysterious warning to Jack before killing his lawyer.

Palmer is alive and well, and has returned to LA for the first time since the attack three years ago. He is running for re-election and is preparing for an important debate with a rival senator. He is accompanied by his brother, who happens to be his chief of staff and his doctor, who also happens to be his girlfriend.

A young boy, Kyle Singer, is seen examining a large, mysterious bag of white powder. He plans to deliver it to some dealers later that day, but he is being watched by Salazar's men.

Kim now works at CTU and has been dating Chase for three months. Kim wants to tell her father, but Jack has a mysterious health problem that may make things more complicated.

Michelle is torn by personal and professional obligations when she must take charge of CTU after Tony is wounded.

Kyle and Linda are captured by Hector's men.

Jack and Palmer have a secret conversation, leading Jack to take drastic action in the face of the Salazars' threat. But Jack's plans are complicated when Chase gets in the way.

Anne pushes Palmer back onto moral ground in the face of her ex-husband's blackmail scheme.