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.

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.

On a call with Station 37, a firefighter is struck by a power line and decides to lash out after her injury. Brett is visited by Scott and Amelia. Violet gets a surprise envelope. The rest of 51 enters a contest.

Boden, Kidd and Severide work together to protect one of their own. At the Fire Academy, Herrmann meets an inspiring young man. Talk of the annual CFD Gala dominates the firehouse.

Severide and Seager team up to investigate a fire at the home of a troubled young woman. Pelham moves into 51's rumored cursed office. Kylie assists Kidd with Girls on Fire.

Chief Hawkins goes above and beyond to help Brett and Violet with a problem. Kidd pursues an open lieutenant position. A blast from the past asks Mouch and Herrmann for a favor.

Cruz forms a bond with a young immigrant boy he meets while fighting an apartment fire. Squad makes plans to prank the newest member of their team.

Severide and Kidd work with CPD regarding a suspicious car wreck. Hawkins and Violet's relationship is in jeopardy. Chloe and Cruz adjust to a new family dynamic.

Firehouse 51 tackles a fire caused by a dropped jet engine, and one of their own is accused of a theft related to the incident. Kidd and Boden disapprove of Kylie's potential new love interest.

A family friend asks Herrmann for some advice on opening a bar. Tensions run high between Emma and Violet. Kidd struggles to keep her team together.

Mouch and Ritter work together to solve a murder mystery. Severide and Cruz tackle a food truck fire. Gallo goes to see Hawkins about Violet.

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.

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.

Javi spends a couple of shifts at Firehouse 51. Kidd and Carver work together to help Carver's former boss. As Hawkins and Violet's relationship blossoms, Gallo turns his attention elsewhere.

Kidd recruits Carver, Capp and Tony to help prepare her new lieutenant's quarters. Severide and Det. Pryma pair up to work a police investigation. Firehouse 51 fights a movie theater fire.