In first episode of 24, Jack Bauer is called into work at the Counter Terrorist Unit, where he learns that an assassination attempt will be made on presidential candidate David Palmer. Meanwhile, Jack's daughter Kimberly sneaks out of the house and his wife Teri sets out to find her.

After a 747 explodes over the Mohave Desert, Jack investigates while he continues to search for Senator David Palmer's potential assassin and the whereabouts of his daughter. Meanwhile, Palmer discovers another threat to his campaign is about to surface.

Kimberly and Janet find themselves in great danger and must look for an escape route. In her search for Kimberly, Teri has found help from Janet's father Alan York. Meanwhile, Palmer attends a secret meeting about disturbing news that is about to break, and Jack discovers a key card that could lead him to the terrorist organization.

Jack's suspicion that someone at CTU may be involved in the assassination attempt on David Palmer causes friction with one of his closest supporters. Meanwhile, Kimberly and Janet's struggle for freedom takes a tragic turn and Palmer ignores the advice of his security team to move ahead with a public appearance.

Following the shootout, Jack goes to the police station to try to get key information from Greg Penticoff. Meanwhile, Kimberly gets handed over to Gaines and Palmer arranges a meeting with reporter Maureen Kingsley.

Jack's wall that separates his work and family comes crumbling down when he discovers Kimberly may have been kidnapped. Meanwhile, Palmer discovers his family has been protecting him from a secret that could hurt his campaign. And Gaines is upset with Dan and Rick and Janet struggles to stay alive as Alan and Teri console each other at the hospital.

Jack's returns to CTU in an effort to keep his wife and daughter alive. Meanwhile, Palmer tries to convince his son that they need to tell their side of the family tragedy, and at the compound, Rick sticks up for Kimberly.

As the California primary officially begins, Senator Palmer wants to rewrite his campaign speech so that the truth of his family tragedy can be revealed. Meanwhile, Jack tries to find the assassin and keep his wife and daughter alive.

Jack's efforts to save Senator Palmer backfire, turning Jack into the primary suspect. He is forced to defend himself or face being turned over to the FBI for questioning. Meanwhile, Teri and Kimberly band together at the compound to help each other cope with being hostages.

Jack, now a wanted man, evades police while working with CTU to find Teri and Kimberly. Meanwhile, Tony and Nina track down information about Gaines as a new Director of CTU takes the helm. Also, Senator Palmer's life remains in danger as those around him do their best to protect him.

Jack goes on the offensive and takes a colleague of Gaines for a wild ride in a limousine to find clues about his wife and daughter's whereabouts. Meanwhile, Rick gets punished for protecting Teri and Kimberly, and Senator Palmer learns about a possible conspiracy within his campaign.

Jack begins closing in on the location where Teri and Kimberly are being held hostage. Meanwhile, Teri and Kimberly create a shock of their own as things get violent at the compound. Also, Senator Palmer's worst fears are realized when he uncovers just how far his campaign backers are willing to go to protect him.

Gaines' boss finally loses patience with Gaines' ineffective pursuit of Jack, as Jack turns the tables. Meanwhile, Nina and Tony learn the plot to assassinate Senator Palmer goes deeper than they thought and Senator Palmer gets surprising news from Maureen Kingsley.

CTU discovers that a backup plan is under way to assassinate Senator Palmer. There are more foreign shooters hired and they may already be in the country. Meanwhile, Palmer must deal with the fact that some people financing his campaign are blackmailing him.

Senator Palmer insists on speaking to Jack face to face despite CTU bureaucratic red tape. Meanwhile, Teri and Kimberly are taken to a safe house guarded by CTU agents.

Jack makes contact with an agent in New Orleans who may have information concerning the assassination conspiracy. Meanwhile, Nina debriefs Teri and tries to get all information that may help with the investigation.

Jack brings in someone from Senator Palmer's staff to help him arrest one of the would-be assassins still out to kill Palmer. Meanwhile, Keith does some of his own investigative work to find out what really happened in the death of Dr. Ferragamo.

While Jack tries to turn up the heat on the remaining shooters, he is forced to work with an overzealous CTU agent. Meanwhile, Senator Palmer must decide what to do with the key evidence Keith obtained about Dr. Ferragamo's murder.

Following the murder of the agent in New Orleans, Jack learns of a location in Saugus that could hold the key to the entire assassination and kidnapping plot. Meanwhile, Kim finds her way back to Rick, who is in some trouble of his own with Dan's hot-tempered older brother.

Dennis Hopper makes his first appearance as a Balkan war criminal who blames Jack for the death of his loved ones. His attempt at revenge is the motive behind the conspiracy. Also, Mark DeSalvo (guest star Lou Diamond Phillips) is in charge of a prison facility where Jack must gain access.

Jack is at the mercy of the criminal masterminds he has been working all day to capture, while Kim must prove her innocence after she is mistakenly swept up in a police drug sting.

Victor and Andre Drazen use Jack as trade bait to get Alexis Drazen back. Meanwhile, Kimberly is again put in harm's way.

"The mole" within CTU is finally revealed. Meanwhile, the Drazens use Kimberly to make Jack do their dirty work.

The action-packed and suspenseful season finale finds Jack in the ultimate showdown with the Drazens. Meanwhile, "the mole" causes more damage than anyone could have anticipated.