When an attempt on U.S. Army Sergeant Eric Carter's life is made after his return home from a mission to kill terrorist leader Bin Khalid, he discovers that he and his fellow Rangers' identities have been compromised. Carter enlists the help of former National Director of CTU, Rebecca Ingram, who quarterbacked the raid that killed Khalid and is one of the few who knew the Rangers' identities. Together they work to uncover a sophisticated terrorist network in a race against the clock to stop a devastating terrorist attack on United States soil.
When Ben Grimes demands money in exchange for the list he seized from a safe box in Khalid's compound, Carter must go back to his roots to help obtain the money. Meanwhile, Rebecca is determined to figure out who leaked the Rangers' files.
After Carter escapes from the police precinct, he must put his trust in the CTU as he plans a meet up with Grimes to do the exchange. Meanwhile, Rebecca and Donovan try to isolate the leak and Amira and Harris deal with a slight hiccup in their plan.
Carter and Grimes try to make a deal with the leader of a smuggling ring in order to find out the location of the terrorists for whom they've been searching. Meanwhile, Amira and Khasan get a visit from an unexpected guest, while progress is made on the leak.
In the season's penultimate episode, Andy uncovers important information about a high-ranking government official, leading Carter and Donovan to team up and find out more. Meanwhile, a reinforcement is brought into CTU to oversee operations.