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.

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 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.

The game changes for Jack Bauer, and the FBI is forced to collaborate with other federal agencies. As the threat intensifies, the administration shakes things up and seeks a new perspective.

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.

Jack Bauer endures the elements and fights on to prevent an attack that could change the country forever. As the catastrophic blow to the nation nears, Tony Almeida operates from the field and Kim Bauer, who was last seen in Season Five, returns. Meanwhile, the stakes are raised when the administration is faced with a blackmail scenario.

The nation remains vulnerable as Starkwood mastermind Jonas Hodges (guest star Jon Voight) remains at the epicenter of the mounting terrorist threat. Meanwhile, the FBI and the administration scramble to provide security and justice, and Jack Bauer questions a key suspect

Presented with the evidence of Olivia's actions, President Allison Taylor is forced to make a decision between her family and the Presidency. Thanks to Kim Bauer, Janis, Renee and Chloe are able to save Jack and arrest Tony before he can kill Alan Wilson. With Wilson refusing to talk and Jack about to die, the fight is no longer in the field, it's for the hearts and souls of Jack and Renee.