Season synopsis
Contains spoilers for this season and earlier seasons.
Three years later, CTU and President David Palmer respond to a virus threat in Los Angeles. Jack Bauer has returned from an undercover operation in northern Mexico with a heroin addiction he acquired to maintain his cover; the investigation soon draws him back into the Salazar family's orbit. The apparent demand to release a prisoner is a path to a real virus auction. Jack's colleague Chase Edmunds is dating his daughter Kim, creating tension as she works at CTU and tries to prove herself. Tony Almeida and Michelle Dessler are now married.
Jack kills Nina Myers during her escape attempt at CTU. A vial of the virus infects a hotel, killing CTU agent Gael Ortega and trapping Michelle among exposed guests. Former government agent Stephen Saunders controls the threat and forces Palmer to meet a series of demands, including the killing of regional director Ryan Chappelle. Jack shoots Chappelle and hands over his body as proof. Jack eventually helps capture Saunders, but Gael’s widow Theresa shoots him at CTU before he can identify the last carrier.
Jack and Chase track the carrier, Rabens, into a school. During the struggle Chase clamps the virus device to his own arm, and Rabens activates it before Jack kills him. Unable to disarm the device, Jack cuts off Chase's hand and seals the vial inside a refrigerator, containing the release. Chase is taken to surgery, and doctors are optimistic about his recovery. Jack tells Kim he supports her future with Chase. Tony is returned to custody for his actions during Saunders's threat; Palmer decides against seeking reelection after Sherry's death and the campaign scandal. Jack leaves the hospital in tears, then answers CTU's call.