Whether giving incoming rookies a brutally frank description of the horrors he's seen and heroes he's known during his many years in the department, or working alongside hardened veterans like Lt. Kenny "Lou" Shea, Tommy Gavin is, first and foremost, a New York City firefighter. Under the command of Chief Ron Perrolli, a gruff, by-the-book department veteran, and his hard-gambling polar opposite, Jerry Reilly, Tommy and fellow firefighters Franco Rivera and Sean Garrity rely on their experience to train rookies like Mike Lombardo, a probationary firefighter, or "probie" -- whose very life rests on how fast he can learn from their experience. Like all of his colleagues, Tommy is called upon daily to risk his life, while trying to cope with the haunting memories of his late cousin, Jimmy Keefe, one of the many firemen who died during the 9/11 attack on the World Trade Center.