As the terror threat continues, the Hassan family turmoil fans the flames of the increasingly urgent situation. When Jack closes in on a person of significant interest, a tense meeting between President Taylor and Omar Hassan takes an unexpected turn as the global security stakes are raised.

Undercover Agent Renee Walker confronts her painful past when attempting to broker a deal with a ruthless, but very well-connected German arms dealer. When CTU shifts its focus from the perilous circumstances surrounding Jack and Renee, lead analyst Dana Walsh comes up with a plan to quell her situation and Chloe O'Brian puts Arlo Glass in his place. As Jack and Renee’s undercover mission takes unexpected turns, the Hassan family turmoil has President Taylor reeling as the peace agreement is jeopardized.

Despite averting the assassination attempt on foreign peacekeeping leader Omar Hassan, Jack Bauer's day intensifies when he is forced to go further undercover to secure the unsecured enriched nuclear materials. As international delegates reconvene at the United Nations, President Taylor's goodwill comes into question and CTU races against time to assist with the mission.

President Taylor's vision of global peace has been foiled over the last 13 hellish hours, and the situation worsens when the imminent threat of mass destruction clarifies. As her idealistic nature becomes a point of contention, she tasks Jack Bauer with a crucial mission, and advisor Ethan Kanin returns in the heart-stopping.

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.

Four explosive hours after being unwillingly drawn back into action, Jack Bauer reteams with a risky Renee Walker to track some very dangerous leads. Meanwhile, back at CTU, a desperate Dana Walsh faces tense and untimely circumstances, and emotions escalate when President Taylor learns of a larger looming threat that jeopardizes the peace accord with President Hassan.

President Taylor pressures CTU for progress while Jack's perilous plan has operatives panicked. As the scope of the looming threat expands, the dynamic at CTU changes and the ongoing crisis worsens.

As Jack's day enters the early morning hours, the nation remains vulnerable, and President Taylor presses on with her international peace process. With the possibility of colossal failure facing CTU, attention turns to who is to blame, and things get personal when operatives take matters into their own hands.

The clock races into the middle of the night when the threat of a devastating nuclear attack accelerates as Jack tracks an informed terror suspect who has an explosive strategy. Back at CTU, a key player grapples with being demoted, and the day takes an unexpected stressful turn when pesky parole officer Bill Prady enters the picture.

As the imminent terror threat nears and CTU copes with the day's explosive events, the onerous NSA intervenes. Conditions at CTU remain tenuous and field operatives find intense action when Jack Bauer leads them on a risky mission. Meanwhile, Chloe and Dana make game-changing moves.

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.

As the day stretches into the middle of the night, Jack and the FBI formulate a plan to prevent further terror attacks. Events take an unexpected turn when the politics surrounding the administration expand beyond the White House.

While the newly-upgraded CTU is challenged by some unexpected and complicated circumstances, Jack Bauer becomes even more involved in preventing an upcoming assassination attempt on Omar Hassan, a visiting President. Meanwhile, international security is jeopardized by an explosive event, and Jack is reunited with agent Renee Walker.

Jack Bauer becomes further involved in preventing an assassination attempt on visiting president Omar Hassan. As the crisis continues to escalate, the crew at the newly upgraded CTU is challenged by some unexpected complicated circumstances. Meanwhile, tensions run high when an explosive event jeopardizes international security.

As dawn breaks over New York, President Taylor endures a game-changing setback as the threat of mass destruction looms. Meanwhile, President Hassan makes a shocking decision that surprises his loved ones. But before long, trusted confidantes will become enemies of the state, and it's only the beginning of the betrayals that are to come as the race against time ticks over two pulse-pounding hours.

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.

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.

For the first time in New York City, Jack Bauer is reluctantly drawn into action as President Allison Taylor negotiates plans for international security with Middle Eastern leader Omar Hassan. As the 8th day keeps unfolding, we learn that CTU, now upgraded and operated by M.B.A.-schooled Brian Hastings, still has Chloe O'Brian, but also expert analyst Dana Walsh and systems analyst Arlo Glass.

While Jack and Cole team up in the field to shield New York from the calamitous threat, a hostage situation has CTU completely stressed out. Meanwhile, unrelenting parole officer Prady presses on in his investigation, and unexpected developments send the Hassan family into a major tailspin.

After Jack convinces Palmer he is not trying to kill him, they go over the "Operation Nightfall" file. The goal of the operation was killing a man named Victor Drazen, and a startling piece of information in the file convinces Jack and Palmer that they are both being targeted. Meanwhile, a scare at the clinic results in Teri and Kim being whisked away to a safe house.

Jack learns that one of the assassins, Alexis Mecir, is actually Victor Drazen's son and has become intimate with one of Palmer's aides. In an attempt to find the man ordering the assassinations, the aide agrees to plant a tracking device in Alexis' wallet. Back at the safe house, Teri and Kim discover their location is no longer secret or safe.

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 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.

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.