Chaon Cross

When a fire claims one of their own, there’s plenty of guilt and blame to go around. Lt. Matthew Casey (Jesse Spencer), in charge of the Truck, tries to carry on, but clashes with the brash Lt. Kelly Severide (Taylor Kinney) of the Rescue Squad -- and each blames the other for their fallen team member. Adding to the turmoil, Casey, unbeknownst to his colleagues, is in the midst of a separation from Hallie (Teri Reeves, "Three Rivers"). The firehouse also includes: Battalion Chief Wallace Boden (Eamonn Walker), a fireman’s fireman who is confronted by important personal decisions; paramedics Gabriela Dawson (Monica Raymund) and Leslie Shay (Lauren German), who share a close bond and team together to face some of the most harrowing situations imaginable; Peter Mills (Charlie Barnett), an academy graduate who is the latest generation in a family of firefighters; and Christopher Herrmann (David Eigenberg), a seasoned veteran who loses his home to foreclosure and now must uproot his family to move in with his in-laws.

Severide is hiding a serious shoulder injury sustained in the fire that killed Andy Darden, and grapples with his guilt as he fights to rescue a construction worker trapped in a building collapse. Adding to the burden, Darden's wife Heather turns on Severide at the annual firefighters' barbecue, blaming him for her husband's death. A call is made to an accident site at Hancock Tower, where two teenagers are pinned in a vehicle trapped beneath the falling debris of a broken window washer's cart. Meanwhile, Casey and Hallie work to figure out their future together.

When a tanker collides into a commuter train that subsequently crashes into a warehouse, the firehouse is called to the horrific scene that tests everyone to the limits as life and death hangs in the balance. With the ultimatum in place for him or the firehouse, Boden (Eamonn Walker) is tasked with making life-changing decisions regarding his future. Severide (Taylor Kinney) learns more about Katie (guest star Brittany Curran), the young woman he saw with his father (guest star Treat Williams). Meanwhile, Shay (Lauren German) and Dawson (Monica Raymund) are still at odds and Casey's (Jesse Spencer) responsibility of being a surrogate father takes a sharp turn.

An arsonist targets Lt. Severide. Meanwhile, Station 51 is under scrutiny by Gail McLeod, a financial consultant for the city who is deciding if any firehouses should be closed. Mouch receives a visit from his Japanese girlfriend, Lt. Casey "celebrates the one-year anniversary of Andy's death, and Shay suspects Severide's paternity.

Boden's (Eamonn Walker) future with Firehouse 51 is on the line and McLeod (guest star Michelle Forbes) keeps on him about his past wrongdoings, pushing him toward an early retirement. With Boden considering his options, McLeod calls on an unlikely candidate to potentially replace him as Chief. Meanwhile, it becomes clearer who the mole inside the firehouse is and everyone takes measures to make their disdain for him known. Meanwhile, Shay's (Lauren German) social life is in full bloom and Arthur (guest star Mike Starr) continues to take money from the struggling Molly's.