Lt. Casey gets off on the wrong foot with Sam Mullins, a temporary Chief who is filling in for Boden at House 51 for the morning. When Casey later makes a risky move in an attempt to save a distraught man from jumping off a building, Mullins has a surprise that Casey does not expect. Mouch flies in Cruz's brother Leon as a birthday surprise, but the rest of the squad struggles to keep it a secret. Meanwhile, Brett is caught off guard when she learns new information about her hometown friend Hope.
No job is more stressful, dangerous or exhilarating than those of the Firefighters, Rescue Squad and Paramedics of Chicago Firehouse 51. These are the courageous men and women who forge headfirst into danger when everyone else is running the other way. But the enormous responsibilities of the job also take a personal toll.
With big reputations and hefty egos, the pressure to perform and make split-second decisions is bound to put squad members at odds. When a tragedy claims one of their own, there's plenty of guilt and blame to go around. In the middle of a divorce, Lt. Matthew Casey tries to go about business as usual, but can't help butting heads with the brash Lt. Kelly Severide of the Rescue Squad - and each blames the other for their fallen team member. When it's "go-time", though, they put their differences aside and put everything on the line for each other. This is a look inside one of America's noblest professions.