The tension has been building inside the firehouse ever since Bennie Severide (guest star Treat Williams) arrived in Chicago, and in tonight's all-new episode, things reach a boiling point when Mills confronts Bennie about the fire that killed his father.
VIDEO - Go Inside The Chicago Fire House
Poor Kelly is also forced to defend his dad to Chief Boden, whose rocky history with Bennie isn't helping matters much. But when father and son discover the truth behind two mysterious diner fires, the station is forced to look at The Severide men with new eyes.
Check out ETonline's exclusive clip from Chicago Fire, airing Wednesdays at 10 p.m. on NBC.