Boden pushes his team to pull it together in the aftermath of the explosion; Casey works to track down a missing Severide; Newhouse brings news about one of Mills' relatives; Herrmann and Otis come up with new goals.
Severide comes back to work, but isn't his usual self; Mills discovers more information about his father's family; Herrmann asks Molly investors to share ideas that could help turn the business around.
The members of Firehouse 51 and the Austin firehouse clash when trucks collide on the way to a call; Boden comes up with a plan to get Dawson her badge; Mills faces his past and future; the Molly's group hits a speed bump starting the food truck.
Dawson tries to find balance with Lt. Casey; Mills deals with a future without the squad; Severide faces his demons; the Molly's crew meets with a city inspector.
Casey deals with the fallout from his sister's divorce; Dawson and Mills settle into their new roles at the station; Brett can't decide what she wants to do; the Molly's crew struggles to get the food truck started.
Casey helps his sister and faces down his corrupt brother-in-law; Brett goes out of her way to assist a mother in need; Mills learns about unlicensed private investigation; Dawson starts training with Herrmann.
Severide wants further investigation when a homeowner saved from a fire is found clutching a suspicious box; Molly's II needs a chef.
The members of the firehouse spring into action when a helicopter explodes over a densely populated area, scattering debris; a dangerous man corners Brett.
Dawson and Casey's relationship is tested as the team responds to a truck leaking hydrochloric acid in a busy intersection; Severide learns about Brittany's past; Mouch has dating troubles.
A house fire puts a couple in danger; Dawson and Casey are pushed apart; the Chicago Holiday Fest gives Molly's II a chance to shine.
Two members of the firehouse go missing after a routine call; Casey and Dawson struggle to balance their personal and professional lives; Boden and Donna learn their baby has potential complications.
Evidence at a storage unit fire seems to be connected to the blaze that took Shay's life; Chaplain Orlovsky is in a car accident.
More clues emerge about the fire that killed Shay, leading Severide to a former nemesis; Shay's sister visits; Cruz is faced with a surprise; Boden tries to help his father.
The pursuit of a missing teenager leaves Mills and Brett stranded in unforgiving elements; members of the firehouse care for an abandoned newborn; Severide receives an intriguing proposal; Boden is at odds with his father (Richard Roundtree).
A temporary chief fills in for Boden, who is forced to take some time off for personal reasons; Lt. Severide deals with an unwelcome addition to the squad; Brett becomes close to a girl she previously rescued; Casey starts seeing a new woman.
Severide steps in when Chief Pridgen tries to shift blame for a tactical error onto Casey; Mouch learns he fathered a child through a sperm donation; Brett and Cruz take Dawson on a double date.
Severide talks to Chief Boden for an old friend who needs a second chance with the fire department; Mills endeavors to regain his active status; Brett and Dawson decide they need a night out.
Herrmann tries to rescue a toddler from a structure fire; Mills discovers unexpected news; Brett and Cruz's relationship reaches a critical juncture; Otis is surprised by some feelings that develop.
Members of Firehouse 51 transport victims of a gas leak to nearby Chicago Med; an armed patient claiming to be carrying a deadly airborne disease forces Chicago Med into lockdown.
Mills works to save the life of a driver injured in a car wreck; Casey harbors doubts about Jack Nesbitt; Hermann, Otis, Cruz and Chaplain Orlovsky ready their team for the peewee hockey championship.
An apartment fire with connections to a rape and attempted murder leads to a joint investigation with the CPD and Sgt. Benson of the NYPD's Special Victims Unit; Dawson risks her life during a call.
Sgt. Voight encourages Lt. Casey to go under cover in order to obtain proof of Jack Nesbitt's shady dealings; tensions grow between Otis and Severide; Herrmann helps another member of the firehouse.
Lt. Casey ends up in danger as he continues to investigate Jack Nesbitt; Boden tries to create unity in the house; Cruz and Boden put their lives on the line to save their own when a warehouse blaze gets out of control; Dawson receives news.