Severide and Violet risk clashing with Paramedic Chief Robinson after Lennox makes a dangerous decision on a call.
Sybil (guest star Nathalie Kelley) enacts revenge on Damon (Ian Somerhalder) by putting him in a catatonic state. Caroline (Candice King) and Bonnie (Kat Graham) enter Damon’s mind and run into familiar faces from the past, only to discover Stefan (Paul Wesley) is the key to Damon’s fate. It’s a race against time for the bell as both Sybil and her sister Seline (Kristen Gutoskie) jockey for its control. Zach Roerig also stars.
The big wedding day arrives and Firehouse 51 welcomes Casey back to celebrate the joyous occasion. Emma's plans to replace Violet come to a shocking end.
In the first part of a three-show crossover event, a rare but deadly bacteria takes its toll on numerous victims around the city, leaving Chicago's finest first responders to work together alongside the CDC to resolve the dangerous situation. Following a fire at a local university that ties into the outbreak, Severide has suspicions that something bigger is happening
A fire at a homeless encampment leaves Severide and Casey searching for answers. Cruz is shaken up after a close call. Ritter lends a helping hand to a victim.