Mark and Amanda are assigned to the task force investigating an airplane crash. An adversarial FBI agent and Russian mobsters make their assignment more difficult.

Steve and Ron lead the chase for the stolen nuclear material.

Dr. Sloan insists that a man he helped condemn to death for a series of bombings is guilty, even after a post-execution explosion.

Three months after the execution of Lewis Sweeney, explosions are still rocking the LA area every four days. The unpopular Dr. Sloan continues his efforts to nail Carter Sweeney for the bombings.

Mark, Steve, Jesse, and Amanda are all trapped in the rubble of Community General in the aftermath of the bombing. Mark tries to shake off the numbing effects of the explosion in time to save Amanda, who's suffering from a punctured lung and broken collarbone. After the dust settles, the hunt for Caitlin Sweeney begins. It's discovered that the Sweeneys belong to a terrorist organization, R.O.A.R.

Carter and Caitlin kidnap Mark, forcing him to mastermind a 100 million-dollar theft. On the outside, Steve and Ron collaborate to find Mark. Meanwhile, Jesse and the Sloans buy a barbecue joint.