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.
Severide and Violet risk clashing with Paramedic Chief Robinson after Lennox makes a dangerous decision on a call. Capp and Tony attempt to break a world record. Cruz and Chloe's marriage problems come to a head.
Firehouse 51 deals with the aftermath of the capsized boat rescue. Gallo, Ritter and Violet discuss plans for a side gig.
After the fatal end to an argument on a construction site, the squad works to untangle facts about the incident. Meanwhile, Riggs struggles to rekindle his relationship with Molly, Trish's job is on the line as she tries to close a big deal at work, and Murtaugh gets one last chance to make it right at home.
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
