Katelynn Shennett

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.

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.

Det. Pryma's case comes to an explosive end with Kidd and Carver's lives in danger. Brett installs an infant Safe Surrender Box at 51. Violet is determined to take Emma down.

A mysterious caller who is in danger relies on Kidd to help save her and her brother; the firehouse helps Cruz get ready for fatherhood.

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