Firehouse 51 deals with the aftermath of the capsized boat rescue; Gallo, Ritter and Violet discuss plans for a side gig.

A video of Casey from the roof rescue goes viral; Mouch sets up a Little Free Library at Firehouse 51; Herrmann breaks protocol.

Griffin learns the truth about his father's death and reveals why he really came to visit Casey; Gallo, Ritter and Violet take steps to expand their microbrewery business.

Kidd spreads her wings as a lieutenant; Chief Hawkins rides with Ambulance 61 to learn more about Brett; Casey takes a trip out of town; a Ritter date night turns into an emergency situation.

Casey makes a life-altering decision; Gallo, Ritter and Violet agree to an interview and photo shoot; Brett and Mouch launch the paramedicine program; Cruz comes closer to fatherhood.

A major security breach in the city's computer networks forces Firehouse 51's senior leaders to take matters into their own hands; Severide gears up for an arson investigation.

Gallo clashes with the new lieutenant temporarily filling in for Casey; Severide closes in on a dangerous and deadly arsonist.

Severide and Herrmann clash over office space; Boden looks at Pelham's past as he considers making him permanent; Gallo's resentment of Pelham comes to a head; Brett and Ritter force Violet to confront her true feelings for Gallo.

Gallo, Violet and Ritter debut their microbrewery business at Winterfest; Brett prepares to present her paramedicine program to an oversight panel; Firehouse 51 gets in the holiday spirit.

Stella Kidd returns to Firehouse 51; the team must work together to put out a potassium fire in a tunnel; after that incident, Ritter begins to worry about a young cop who witnessed the fiery death of a truck driver.