Tracy Spiridakos

The team investigate a drug deal gone bad after the body of a college student is found; Detective Hailey Upton temporarily joins the team and finds her investigative methods clash with the Bureau's more buttoned-up environment.

Kidd and Severide's honeymoon is interrupted by a dangerous person from their past; Kidd's former academy classmate joins Firehouse 51; Brett and Violet reflect on their relationships.

Mouch builds a classic fire truck model for the deputy district chief but needs assistance from Gallo and Ritter; Brett and Violet encounter multiple victims with a strange set of symptoms; Cindy's chemotherapy results loom over the Herrmann family.

Mac joins forces with special agent Jack Dalton to recover a missing bioweapon and save hundreds of thousands of lives.

The Hellcats team accompanies Savannah on her first date with Dan; Marti tries to impress her law professor in hopes of joining his legal team; Alice turns to pills; Vanessa decides to come clean with Derrick.

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; Severide suspects something bigger is happening.