Firehouse 51 is in an uproar over the death of Andrew Darden and the mutual recriminations of Lts. Casey and Severide. Enter rookie Peter Mills, a second-generation firie intent on facing down the element that killed his Dad. Also part of the team are paramedics Lesley Shay and Gabriela Dawson. Battalion Chief Wallace Boden, rules this quarrelsome crew with an iron fist, ensuring that they pull together, when the chips are down, to keep the city safe.