Tommy Gavin and company face new challenges and old demons as they roll back into action for a fourth season of Denis Leary and Peter Tolan's series. As the season begins, Tommy is in the fight of his life, defending himself against arson and insurance fraud. He struggles to raise his new baby while facing paternity questions and fighting to keep his family together. Franco seems ready to settle into a steady relationship, but is shaken when he loses custody of his daughter. Alcoholism has taken a toll on Sean and Maggie's marriage, while Lou's newfound love threatens to put him in the hospital. And Chief Reilly fights back from a stroke only to find himself facing a decision that could change the fate of Truck Company 62 forever.