Season five starts 18 months after Jack Bauer was forced to fake his own death and go underground. Now living under a false name and working in an oil field, Jack leads a quiet life, renting a room with a woman and her son.
Just as President Logan is about to sign a new arms treaty with Russia, an assassin targets the only four people who know Jack Bauer is still alive - and he's forced to return to Los Angeles.
As Chloe helps Jack sneak into Palmer's apartment to look for clues, the CTU figures out he's still alive; and Martha continues to insist that Palmer was trying to contact her about a matter of national security.
As the CTU sets up to storm the airport, the terrorists begin killing hostages; Jack scrambles to save Derek, who's been selected as the next to die; and Martha searches for a transcript of Palmer's phone call.
While being held captive by the terrorists, Jack tries to send a distress message to the CTU; Logan and Suvarov sign the arms treaty; and Martha continues trying, unsuccessfully, to get Logan's attention.
The CTU agents discover that terrorists escaped from the airport with nerve gas; an assassin targets Jack; and Martha thinks she's about to be committed.
After disclosing his connection to the terrorist plot, Cummings convinces Logan to have Jack and Novick taken into custody; and the CTU searches for the missing gas canisters.
Jack and Curtis storm Rossler's penthouse; Erwich finds a mechanic to cut open the cylinder casing; Tony learns of Michelle's death; and Logan prepares to take responsibility for Cummings' misconduct.
Now that Jack Bauer has exposed and interrogated the administration's link to the terrorists, President Logan reinstates him to CTU on a provisional basis. Meanwhile, First Lady Martha Logan grapples with the positioning that her husband and his advisers are planning to take and Jack and CTU operatives attempt to keep the military-grade nerve gas from taking innocent lives.
Head terrorist Vladimor Bierko tries to get his plans back on track by killing both Erwich and Nathanson (who calls Jack for help) - and enlisting Logan in a plan to assassinate president Suvarov.
As Ostroff prepares to attack the motorcade, Logan learns Martha's in the limousine but decides not to intervene; Audrey engineers Lynn's removal from control of the CTU; and Jack falls into a trap at Omicron.
Martha struggles with her feelings after realizing Logan didn't try to save her; Jack goes to Christopher Henderson's home, looking for clues; and the CTU rushes to head off a nerve-gas release at a large hospital.
As Jack is reunited with Kim and interrogates Henderson, the Vice President argues for martial law; Lynn learns of his sister's murder; and Ostroff sets off a Sentox gas canister in the CTU.
After the gas release at the CTU, Jack struggles to ventilate the offices before the safe rooms are breached; Tony wants to kill Henderson; and Gardner urges Logan to declare martial law.
Homeland Security's Karen Hayes takes over command of the CTU; Jack captures Collette with Stoller's help; and Wayne Palmer is pursued on his way to meet with Agent Pierce.
Jack refuses to believe Audrey cooperated with the terrorists; Bierko's men prepare to release more Sentox at a gas distribution center; and Wayne Palmer flees the commandos who are trying to kill him.
As Homeland Security takes over the CTU, Jack and Wayne Palmer go after Christopher Henderson, who has kidnapped the young daughter of Martha Logan's assistant; and Audrey signs away her own integrity to help Chloe keep her job.
Jack and Wayne kidnap a bank manager, and break into the bank where Evelyn stored the evidence against Logan; Henderson searches for Jack; and Karen has Audrey followed.
Having secured President Logan's incriminating tape, Jack delivers it to Secretary Heller; shockingly Heller turns on Jack, and in the process endangers Audrey; Jack must choose between her life and the vital recording.
To save Audrey's life, Jack hands over the tape to Henderson; Secretary Heller makes the ultimate sacrifice; and Jack follows the tape to a diplomatic jet ready for takeoff.
Chloe is secretly helped by an unexpected source at CTU while Jack, trapped on a plane bound for Germany, franticly searches for the tape recording; to protect his presidency, Logan must give his most desperate order yet.
To avoid being shot down by presidential order, Jack forces an emergency landing on an LA freeway; with the incriminating recording delivered to CTU, Logan prepares to take his own life, until Miles offers him an alternative solution.
Miles destroys the evidence against Logan; Martha saves Agent Pierce from certain death; and Bierko hijacks a visiting Russian submarine armed with twelve, multiple-warhead missiles.
Jack and Henderson wage an assault on the submarine as Bierko prepares to launch an attack against L.A. Chloe brings in someone from her past to aid her. Martha and Pierce enlist Novick's help in their plans to expose Logan.
Agent Jack Bauer seeks to avenge the painful loss of innocent lives.