While out on a jog, Severide comes across a secluded and empty construction site and encounters a young boy who has been trapped in a backhoe loader and is in dire need of assistance. Boden and McLeod continue to butt heads about the future of the firehouse and Boden breaks news about his future to Casey. Meanwhile, it's election day for the union presidency and Mouch and Greg Sullivan have a debate on Otis' podcast. With rival bar Game Day's future in peril, the finger is being pointed at Molly's.
When the shooting of a young girl happens in their neighborhood, Cruz and his brother Leon are forced to think about the gang they have tried to escape. The battle between Chief Boden and McLeod continues to escalate and Isabella convinces Mills to dress up for a fancy gala. Meanwhile, Lt. Casey is sad Dawson won't be coming by as much now that his parental duties are over, Shay is fed up with the firehouse and digs in deeper with Devon and Zoya's visa is expiring, prompting her to come up with an idea.
Battalion Chief Boden prepares to counterattack McLeod in a final effort to save the firehouse from closure and the romance between Dawson and Casey escalates. Leon is making progress in the gang murder investigation, but Cruz cannot stand being left in the dark by Voight, fearing for his brother's safety. Meanwhile, Severide and Katie bond to make up for lost time and Otis feels uncomfortable living with Severide and Shay after Devon's latest escapade.
All seems lost with firehouse 51 on the verge of closing its' doors, thanks in no small part to Gail McLeod, but Chief Boden and the rest of the house refuse to allow themselves to sit by and let it happen. An emergency call to an apartment structure fire tests everyone's limits and puts the squad in harm's way. Meanwhile, Dawson receives some life-changing news and union president Greg Sullivan makes headlines, which has an immediate impact on Mouch.
Lt. Casey returns to work at Firehouse 51 after nearly being killed in a building collapse and Shay meets Allison Rafferty, her new partner, who is friendly to everyone except her. Dawson begins her rigorous training at the Chicago Fire Academy, while Lt. Severide prepares for his stint as instructor. Meanwhile, Clarke stubbornly does not speak with the police about the murder in which he is the prime suspect and the future of Molly's looks bleaker than ever.
Lieutenant Casey tries to convince himself and everyone around him that he is one hundred percent healthy following his near-death incident in the line of duty. Shay, not wanting to delve into the emotionally traumatic incident, continues to elude a lawyer who wants to speak with her about Darryl's suicide. Meanwhile, Otis and Katie bond over board games, Boden helps out a woman with a negligent landlord and Dawson notices fellow recruit Rebecca Jones undertaking some interesting test-taking techniques at the Academy.
When a drunk driver knocks down a transformer, the entire neighborhood is left without power on a frigid Chicago night and members of Firehouse 51 step up to lend their much needed help. While many from the community ride out the night at the station, in the midst of such close quarters, romances speed up and tempers flare. Meanwhile, Casey continues to lie to both himself and Dawson about his condition and the stakeholders in Molly's bicker about the bar's direction.
Severide feels sidelined as he leaves Detective Lindsay and the Intelligence Unit to do their job and locate his sister Katie. Shay gets an unusual tip from Chicago Blackhawk players Brent Seabrook and Duncan Keith, who make friends with Clarke and stop by Molly's. Meanwhile, Casey learns more about his head injuries after another close call and Dawson pushes hard to pass the physical test at the Academy.
Severide is getting impatient with the police as Vince Keeler walks free. Meanwhile, the house pulls out all the stops to save a girl trapped inside a donation bin, Mouch learns that Boden's secretary Connie is not someone to mess with and the squad and truck are called to a serious high rise fire inside a 20-story downtown office building.
Lt. Severide (Taylor Kinney) hits the top of the list as Det. Lindsay (guest star Sophia Bush) starts calling in suspects with the clearest motives to make the guy who kidnapped Katie disappear. Meanwhile, Jones (guest star Daisy Betts) is still having trouble fitting in as word of her disruptions reach the fire department's headquarters. Elsewhere, Herrmann (David Eigenberg) celebrates his twentieth anniversary with his wife, but no one supports his idea on the gift he intends to give.
Lt. Severide (Taylor Kinney) is reminded of his own past by a man he saves from a car accident (guest star W. Earl Brown) and feels compelled to help him. Elsewhere, Lt. Casey (Jesse Spencer) and Chief Boden (Eamonn Walker) grapple with how to dock Jones (guest star Daisy Betts) per her father's orders. Meanwhile, Mouch (Christian Stolte) and Dawson (Monica Raymund) have troubles with the opposite sex and an emotional call to duty creates ripples throughout Firehouse 51.
Lt. Severide sticks his neck out for Dave Bloom, a fellow firefighter from Denver who is troubled by addiction. Elsewhere, Dawson and Shay leave town for a "girl's weekend" at a cabin in the woods. Meanwhile, Jones struggles with the knowledge that her father is pressuring Chief Boden about her career path and Mouch's Internet dating profile gets an upgrade with the help of Mills and the guys.
A suicide note is delivered to a surprised Dawson (Monica Raymund) and Lt. Severide (Taylor Kinney) digs deeper into Bloom's (guest star W. Earl Brown) dark past. Elsewhere, Chief Boden (Eamonn Walker) learns shocking news, and with the help of Shay (Lauren German), Lt. Casey (Jesse Spencer) goes on the search for a life-changing item.
With everyone's support, Dawson (Monica Raymund) makes final preparations to retake the fireman's exam, but a call to the field may throw a major wrench into her plans. Elsewhere, Lt. Casey (Jesse Spencer) has an important matter to discuss with Antonio (guest star Jon Seda, "Chicago P.D."). Meanwhile, Lt. Severide (Taylor Kinney) and the firehouse welcome Rick Newhouse (guest star Edwin Hodge), the latest addition to the squad, Shay (Lauren German) gets an uninvited surprise guest and Chief Boden (Eamonn Walker) makes a bold move.