Mo Gallini

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.

Dhan spearheads the search for a missing homeless man who’s been an integral part of a tight-knit encampment. When Det. Trent shares troubling news about Sir, Gabi goes to great lengths to protect her secret.

When an ER physician is gunned down in the street, Castle and Beckett soon discover that the victim was a mob doctor to a Mafia family run by an old friend of Castle's. Also, against this backdrop of Christmas, Esposito and Lanie reach a defining moment in their relationship.

Director Shepard takes a huge risk and agrees to meet an informant alone about Le Grenouille, but the meeting goes bad and her contact is killed.

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.