several months after foiling a terrorist attack on Dodger Stadium, FBI agent Darwyn Al-Sayeed is about to start a new life as a teacher at Quantico when he is asked to investigate a new terror suspect. Former cell leader Farik is interrogated by the CIA.

Darwyn struggles to maintain his cover as he assumes command of a new Los Angeles sleeper cell and questions the experience and skill of his new FBI case agent. Farik's interrogators use new techniques to get him to talk.

Ordered by the terrorist network to acquire a powerful weapon, Darwyn finds the FBI unwilling to cooperate. Ilija faces a heartbreaking decision as he prepares to flee for Europe. Farik is expatriated to Saudi Arabia, where he can be tortured.

The future of Darwyn's cell is altered when he urges the FBI to intercept a shipment of nuclear material arriving at the Port of Los Angeles - sent by none other than Farik; Ilija faces his past when he arrives home in Sarajevo.

The cell's new leader, Karrar, pushes Darwyn aside as plans progress for the nuclear attack on Los Angeles; Farik teaches a lesson about the terrorist way of doing business to an American philanthropist at a school in Yemen.

The FBI and Darwyn move to intercept the cell's plans to detonate a pair of nuclear dirty bombs in Los Angeles on the Fourth of July, but their victory is overshadowed by a pair of tragedies for Darwyn.

Darwyn blames himself for the tragedies that occurred on the Fourth of July and embarks on a suicide mission to Yemen, where he plans to find and confront Farik using his former cell leader's wife as bait.