At the site of a train accident, Peter Mills becomes deeply upset when he observes the dead body of a young victim. Unable to shake his emotional distress about the event, he questions his future as a firefighter. Dawson and Shay save a 6-year-old girl whose mother is abusing her - but their confrontation leads the woman to resort to dire actions. Meanwhile, Severide aggravates his injury while rescuing a heart attack victim and Shay sends Clarice, her married, pregnant ex-girlfriend, back home to her husband.