Counter Terrorist Unit agent Jack Bauer is assigned to protect presidential candidate David Palmer from a potential assassination attempt. Unfortunately, his daughter has disappeared and someone within CTU may be involved. Mandy seduces Martin Belkin, a photographer headed for a meeting with the Senator.

Jack rushes to the aid of CTU Director Richard Walsh who comes into possession of a keycard and ends up in a shootout. Gaines encounters trouble acquiring Martin Belkin's ID from Mandy. Elsewhere, Kim realises the gravity of her situation.

As Kim and Janet temporarily escape their captors, Senator Palmer learns that his son may have been involved in the death of his daughter's rapist 7 years ago. Gaines finally gets Belkin's ID from Mandy, while Jack delivers the keycard to CTU.

District Director George Mason (Berkely) shuts down CTU forcing Jack to escape in order to follow up on a lead on a conspirator. Nina and Jamie try to cover for him. Palmer discovers how a reporter found out about Keith. Jack finally learns that Kim and Janet have been kidnapped.

Jack follows the arrested conspirator to the police station in order to get more info on Kim's whereabouts. Palmer meets with a reporter who has some damaging information. Kim realizes just how dangerous Ira Gaines really is.

Jack meets up with Teri at the hospital where they wait to talk to Janet about Kim. However, Janet is killed by Alan who is really working for Ira Gaines. Palmer confronts his family about the cover up. The body of the real Alan York is found near CTU by Nina Meyers.

Jack returns to CTU to switch out the id card with a fake per Gaines' orders. Palmer tries to convince Keith and Sherry to go public about the murder.

Jack delivers the briefcase to the assassin at Palmer's press conference. Palmer wants to let the press know what happened with Keith and the murder.

Jack is taken into custody by the Secret Service after he stops the assassination. He quickly escapes in order to check on another name from the key card. Palmer tries to deal with the assassination attempt.

Jack is on the run after escaping custody and rushes to intercept Ted Cofell before he leaves the city. Nina receives a phone call from Teri and tries to trace the call. Palmer still wants to go ahead with the press conference despite objections. Alberta Green temporarily takes over as Director of CTU.

Jack takes Ted Cofell hostage after finding his name on the key-card and tries to get whatever info he has about the conspiracy which only amounts to the name of another conspirator, a one Kevin Carroll. Palmer starts to piece together his connection to Jack. Gaines receives orders to kill Teri and Kim from his boss Andre Drazen.

Kevin Carroll (the man who pretended to be York) leads Jack to Gaines' compound where he is quickly discovered. Nina and Tony try work around Director's Green's strict new protocols to help Jack. Palmer discovers that Carl Webb, one of his financiers is handling the Keith situation his own way.

Jack has a final confrontation with Gaines as a CTU chopper heads to the compound. Nina and Tony talk to Jamey's mother in order to learn why she was helping the assassins. Carl Webb threatens Palmer to keep quiet about the murder once and for all. CTU learns that more assassins are on their way to LA.

Director Green and Regional Director Ryan Chappelle question Jack about the day's events. Nina takes Kim and Teri to a safe house after getting them medical attention. Palmer wants a meeting with Jack.

Palmer and Jack finally meet for the first time and discuss Operation Nightfall. Nina talks to Teri about her and Jack's past relationship after they reach the safehouse.

After handing out photos of all the assassins, Jack and Mason discover that one of Palmer's campaign staff is in a romantic relationship with Alexis Drazen. Teri and Kim are attacked in the safehouse. Keith confronts Carl Webb about the cover-up.

Jack and Mason use Palmer's campaign staffer Elizabeth Nash in a sting against Alexis Drazen which backfires badly on them. Kim makes a run for Rick's house after getting separated from Teri following the attack.

Jack poses as Alexis Drazen and goes to meet a contact who has vital information. However, a CTU agent with a grudge against Jack might risk the success of the mission. Dr. Parslow takes Teri back to the Bauer house.

Jack and Mason search for location of the address found in Victor Drazen's confidential file. Palmer finally lets the press know about Keith's past. One of Drazen's goons closes in on Teri; Kim is arrested after the police raid Rick's house.

Jack discovers a top secret detention center houses someone from his past. Tony takes Teri back to CTU as Kim finds herself in jail. Andre Drazen and his soldiers raid the detention center.

Jack is captured by Victor Drazen and Andre when they escape the detention center. Palmer learns he is dominating the California polls. Drazen's men capture Kim after she is released from jail.

In order to buy himself more time Jack puts Victor and Andre in contact via Mason with a hospitalized Alexis Drazen. Palmer becomes involved with a campaign staffer. Tony and Nina learn that Kim has been recaptured.

Jack delivers a cell phone that is unknowingly rigged to explode to Palmer. Kim manages to escape. The identity of the real mole inside CTU is exposed.

Jack Bauer heads to the docks for a final climactic showdown with Victor Drazen.

It's been a year since Jack lost his wife, and the emotional toll includes estrangement from his daughter Kim, who is now a live-in au pair for a troubled family. Jack is no longer with CTU, and no longer interested in that line of work - until he's summoned directly by President Palmer. The situation: terrorists have planted a nuclear device somewhere in Los Angeles and plan to detonate it within 24 hours.

Jack reestablishes his undercover identity to join a crew of suspected terrorists that may know something about the nuclear device planted in Los Angeles. Posing as career criminal Jack Roush, his only hope in proving his loyalty to them lies in the package he's carrying. Meanwhile, President Palmer deals with a curious press, including one particularly skeptical reporter; Kim tries to protect Megan from her father; and Kate Warner follows up on suspicions about her sister's fiancé.

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.

Jack meets with the surviving Coral Snake Commando, who demands Kate Warner in exchange for evidence about the recordings. Tony and Carrie spy on Michelle when he suspects that she is working with Jack. Mike and the Vice-President turn up the pressure on Palmer, when he expresses his doubts about the impending war.

Jack, Kate and Wallace fight to escape from a deadly band of commandos. Palmer decides to take a stronger stance against the civil unrest resulting from the bomb explosion. Tony's trust in Michelle is broken when he suspects her of betraying him. Kim's worries seem to be over when she learns the charges against her have been dropped.

Jack is captured and tortured by men who want the chip. Kate and Yusuf run into a group of angry rednecks before they can deliver the chip to CTU. Tony and Michelle share a tender moment after her brother flips out. Palmer leans towards holding off the attacks, while Lynne discovers a secret operation that the Vice-President is planning against Palmer.

Jack finds an ally who may help him escape from Kingsley's men. Lynne meets with foul play before she can warn Palmer of the conspiracy against him. Chappelle interferes with Tony's efforts to assist Jack. Kate offers her captors money in exchange for the chip.

Palmer's cabinet invokes the 25th Amendment in an attempt to remove him from power. They place him on trial for his extreme actions during the nuclear bomb threat. Jack and Michelle work against the clock to prove that the evidence against the Middle East is false.

Jack locates the man who forged the audio evidence, but his efforts to break him down are sabotaged by Sherry Palmer, who has a hand in the conspiracy. Kim returns to the Matheson home, where she discovers that her problems are far from over. Palmer searches for an ally who will help him get a message out to CTU. Tony and Michelle take Chappelle out of action when he hinders their efforts to help Jack.

When Jack hits a dead end with his lead, he realizes he must persuade Sherry to help him get evidence against Kingsley. Things go awry at CTU when Division becomes suspicious of Chappelle's absence. Michelle goes off-site to work with Jack. Mike and Prescott ask Palmer to aid them as the bombers get closer to their targets.

Jack and Sherry Palmer prepare for a dangerous meeting with the head of the war conspiracy at the L.A. Coliseum; David Palmer sits in as the Cabinet waits for confirmation of the Cypress Chip's invalidity; the air strike on the Middle East draws nearer; the conspiracy goes to an old agent to put Palmer out of play.

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.

Jack and Chase quarrel over Chase's relationship with Kim. Meanwhile, they learn of a lead to the possible whereabouts of the virus after raiding a crack-house.

Linda breaks up with Kyle when she learns that he is planning to make a drug delivery.

Wayne approaches Palmer with information about his girlfriend that could damage his chances for re-election, while a CTU employee is not what he seems.

Jack and Hector both search for Kyle, while Chase finds himself out of action at CTU.

Wayne and Palmer argue over the implications of Anne's past, while Ramon takes out one of his opponents in a surprise move.

Tony leads an operation to get Kyle, but tragedy strikes when Salazar's man gets there first.

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.

Jack's efforts to break Ramon out of prison go awry when they are captured by a group of inmates during the riot.

Chloe unwittingly stumbles on to Jack's drug problem and she is forced to reveal his secret to Kim and Michelle.

Palmer begins his debate with Keeler, while Kyle prepares to sacrifice himself to save Linda.

Jack and Ramon struggle to evade the authorities, while Palmer must shut the debate down because of the prison break.

Kim accidentally stumbles on to Gael's secret communications, but she isn't able to warn Michelle in time.

The Singer family learns a startling piece of news about Kyle's health.

Ramon holds Jack hostage as he flies to Mexico. Ramon plans to kill Jack, but Jack manages to hold him at bay until the plane lands. Ramon then learns that Jack and Hector are working together to break him out of prison.

Gael is captured while trying to escape from CTU. Chappelle interrogates Gael but is interrupted by Tony, who claims that Gael is part of a bigger plan.

Anne is given a chance to clear Palmer's name, while Chase heads for Mexico to rescue Jack.

Palmer and Chappelle view a message from Jack, explaining his undercover work with the Salazars. Meanwhile, Hector tries to convince Ramon that they should deal with Bauer so that they can get their hands on the virus.

Jack has a private moment with Claudia and she blasts him for leaving her behind when he arrested Ramon.

Chase arrives in Mexico, but is captured by Hector's men. Ramon devises a way for Jack to prove his loyalty to them.

Anne manages to clear Palmer's name, but she breaks off her relationship with him.

Palmer clears Anne's name with the press, but he finds that he is facing a new problem when his biggest campaign contributor reveals a startling secret about Wayne.

Kim and Michelle worry about Tony's mental ability when he continues to make mistakes.

Jack and the Salazars meet with Amador, but the deal turns sour when Nina Myers appears on the scene and competes for the virus.

Claudia manages to free Chase from his captors, but she pays a high price for her efforts.

Wayne turns to Julia, while Palmer calls on Sherry for help against Milliken.

Jack and Ramon make plans to get to Nina, in the hopes of intercepting the virus.

Chloe's work at CTU is disrupted when she is forced to take care of her baby.

Jack forces Nina to work with him to get the virus from Amador.

Palmer meets with Sherry and convinces her to help him deal with Milliken.

Chase remains in Mexico to help with the capture of the virus.

Ramon and Hector quarrel when Hector wants to pull out of the deal.

Things finally come to an explosive head as Jack, Ramon, Nina and Chase all close in on the virus. But the deal takes an unexpected turn when Amador pulls a fast switch.

Kim becomes suspicious of Chloe when her story about her baby doesn't check out.

Sherry finds a witness who can damage Milliken, but her advantage is short-lived.

Jack and Chase interrogate Nina, but the worm turns when she causes havoc with the CTU computer systems.

Chappelle puts Chloe under guard when she refuses to answer questions about the baby, but is forced to release her when she is the only one who can deal with the crisis.

Sherry takes her battle directly to Alan, forcing Julia to act as her accomplice.

Tony interrogates Nina about Alvers' location, while Chappelle orders Jack to undergo a medical examination in light of his drug use.

Kim and Chase have a conversation about the baby.

Palmer confronts Sherry about Alan Milliken's death, while Julia begs Wayne for help.

Chappelle threatens to pull Jack from the investigation for killing a material witness, but Jack persuades him to hold off when they find a fresh lead on Amador's whereabouts.

Amador and Alvers meet with the man who is planning to unleash the virus in LA within the hour.

Michelle and Gael locate the target area, but things really hit the fan when they attempt to capture Alvers in the process of releasing the virus.

Wayne argues with Sherry over the consequences of Milliken's death as the police turn up the heat on Julia.

Jack and Chase track Amador in the hopes that he can lead them to the man behind the virus attack.

Michelle faces a mob riot when the hotel is quarantined.

Sherry extorts Palmer, forcing him to manufacture her alibi for the police.

Saunders begins making demands on the President. He forces Palmer to hold a strange press conference and then orders the death of the CTU agent who can trace him.

Jack learns of a woman who can lead him to Saunders, but a surprise attack shifts the balance of power.

As Gael's symptoms get worse, Michelle devises a way to relieve the suffering of the victims at the hotel.

Jack and Chase race against time to capture Saunders before the deadline, while Chappelle plans an escape.

Michelle begins a frantic search when she learns that an infected hotel guest may have slipped through her fingers.

Jack reluctantly works with Kim on an undercover job that may help them gain an advantage over Saunders.

Palmer informs his cabinet of the crisis, while Saunders makes yet another demand.

Chase tracks down the man who left the hotel and learns that the virus is spreading to the general public.

Jack attempts to use Saunders' daughter as leverage to gain control of the virus, while Palmer must deal with the discontented press.

Michelle gets the results of her test, while Adam finds that the virus has struck too close to home.

Tony finds himself compromised when Saunders exploits his only weakness.

Tony works to free Jane from CTU before Saunders can harm Michelle, but Chloe and Jack become suspicious of his activities.

Sherry meets with Palmer's political rival and proposes a deal to blackmail him.

Jack and Tony clash as the time for the hostage exchange draws near.

Keeler meets with Palmer and demands his resignation, while Wayne begins a secret operation against Sherry.

Jack pushes the envelope in an attempt to force Saunders to disclose the location of the missing vials.

Sherry meets with David to discuss her terms, while Wayne breaks into her home to find the incriminating evidence.

Tony finds himself facing a harsh penalty because of his efforts to save Michelle.

Jack and Chase must make a powerful sacrifice when dealing with the virus.

Tony is able to help Jack one last time before he is taken into custody, while an angry victim seeks vengeance on Saunders.

Palmer makes a surprising career choice in the wake of Sherry's death.