Members of the Chicago Firehouse 51 are shaken after the loss of firefighter Andy Darden. Truck leader Matthew Casey and Rescue Squad leader Kelly Severide blame each other for Darden's death. However, they have to overcome the frictions when another colleague, Christopher Herrmann, is gravely injured. Meanwhile, Paramedic Gabriela Dawson performs a risky procedure in the field, in order to save a little girl's life; Casey goes through a rough patch with his fiancée Hallie; and the new candidate, Peter Mills, reports for duty.
When a construction site collapses, a dying workman asks Severide to send his wife a message. Matt decides to work things out with Hallie. The firemen welcome Nicki, a charming young woman who will be working in payroll and who seems to have a thing for Kelly. The Truck members wonder why their crest is a goat.
The firemen respond to a T-bone car accident that leaves a kid paralyzed. The drunk driver that caused the accident is the son of Det. Voight, a dirty cop who wants to cover it all up. However, Casey is determined to expose the truth, despite Voight's threats. Severide finds out what is causing his increasing arm pain; he also hooks up with Nicki and gets caught by her father. Also, Peter decides to quit his side job at his family's restaurant, but his mother is not happy with this career choice.
A homeless man dies in a warehouse fire. Peter Mills might have saved him if he had another minute, but Chief Boden had called everyone outside, as the building was about to explode. Boden knows he did the right thing, but the victim's brother threatens to sue the city. Meanwhile, Det. Voight goes to the next level in his attempt to intimidate Casey; Kelly finds it suspicious that an old lady has been having several accidental fires lately; and Leslie learns some surprising news about an old girlfriend.
Kelly's arm problem worsens and he turns to an ex for help, as she happens to be a pharmaceutical rep. Gabriela risks suspension after hitting a patient's friend. Meanwhile, she bonds with Peter over food. Herrmann becomes involved in a pyramid marketing scheme. Also, Matt gets tired of Voight's harassment and decides to fight back, even though both Hallie and Chief Boden warn him not to do anything stupid.
Gabriela prepares for her suspension hearing and Casey for his deposition. When it becomes obvious that Voight would do anything to protect his son, Hallie and Matt fear for their lives. Casey's only hope is that Det. Antonio Dawson can stop Voight before it's too late.
Between a meth lab explosion, a gang shooting, a turkey fire and a 10-car pile-up, the firehouse is very busy on Thanksgiving. Meanwhile, Chief Boden wants to help a damaged kid, Otis starts a podcast, Leslie's ex-girlfriend pays her a visit, Matt and Hallie have another talk about their future, and Severide risks getting in big trouble when the Chief orders everyone to take a drug test.
After seeing the remains of a victim crushed by a train, Peter is shocked and considers leaving the station. Gabriela attracts her superiors' wrath again, when she accuses a mother of poisoning her daughter. Kelly's addiction to painkillers spirals down, Leslie is confronted by Clarice's husband, and Mouch is very unfriendly to some Canadian visitors.
After inhaling magnesium shavings at a fire, Vargas gets a severe pulmonary injury, forcing him to retire from his job. Chief Boden fears that 14-year-old Ernie is behind several recent dumpster fires. Cruz's attempt to get his little brother out of a gang backfires. On a lighter note, Gabriela asks Matt to come over and repair her window, while Severide receives a dinner invitation from Renée, a very attractive woman that he saved from a car accident.
An Internal Affairs investigation is launched when a woman accuses the firemen of stealing a diamond necklace from her home during a kitchen fire. The lead investigator is an old foe of Casey's. The Chief interrogates Shay and Dawson about some narcotics that went missing from the ambulance. Joe Cruz is faced with a big moral dilemma while trying to get his little brother out of a gang. Gabriela asks Matt out on a date, and things heat up between Kelly and Renée.
Gabriela struggles between her crush on Matt and her budding romance with Peter. Kelly comes clean to the Chief about his arm; he also learns that the surgery's consequences might be even more severe than he'd thought. Casey's mother asks him to speak up for her at the upcoming parole hearing. Meanwhile, the calls of the day include a plane crash and a van full of illegal immigrants that were left to die.
After learning that an experimental surgery could significantly reduce his recovery time, Kelly starts having second thoughts about his decision to move to Madrid with Renée, and he asks his dad for advice. Matt speaks for his mother at the hearing. Chief Boden tries to save Ernie, the damaged kid, but it might be too late. Otis is sent to fill in for someone at another firehouse. Peter brings a puppy at the station. Also, Clarice comes back in Leslie's life.
One month later, Severide returns to the station after a full recovery, only to find out that the person who filled in for him is his ex-fiancée's brother. Otis reconsiders his decision to transfer. Herrmann, Gabby and him buy a bar. Casey's mother is released on parole and moves in with her son. Gabby sends a text to the wrong person. Clarice goes in labor. Also, there's a spike in heroin overdoses and Gabby's brother Antonio is determined to go after the guys who are behind it, no matter what it costs him.
In order to help her brother, Gabriela contacts an old enemy, even though this could ruin her friendship with Casey. Herrmann retaliates when Arthur, the silent partner from the bar, attempts to intimidate him. Leslie and Clarice try to avoid a custody lawsuit with Daniel. Severide tracks down his ex-fiancée, and Casey confronts his mother about the reason why she killed his father. The firehouse responds to a drowning kid and a collapsed house.
To make up for the crushing feeling of guilt, Cruz becomes overzealous at work, to the point where he puts a colleague's life at risk. Otis, Herrmann and Gabby find a hidden safe in their bar. Kelly finally confronts Renee Whaley. Casey meets with his sister to decide what to do about their mother, who has been acting quite recklessly. Meanwhile, Leslie struggles to prove she could be a fit mother to Clarice's baby, but to make matters worse, a homeless man sticks her with a needle, possibly exposing her to HIV.
After her break-up, Shay decides she wants to have a baby by herself. Gabby, Herrmann and Otis track down the owner of the box they found in the safe. At the scene of an accident, Peter Mills bravely talks a man out of suicide. Later, at the annual Academy Dinner, Gabby and Peter come out as a couple, Gabby overhears Benny Severide reveal a big secret about the death of Peter's father, and Andy Darden's widow surprises Casey.
Peter starts looking into his father's death and he confronts Benny Severide about it, while Chief Boden asks Gabriela to keep a secret. After an unexpected source tells her more about the sperm-donating process, Shay decides to take a different approach at having a baby. Kelly wants to help an old man whose restaurant has been put on fire as an intimidation method, but nothing is at it seems. Heather invites herself to dinner with Matt.
Matt is upset that Kelly wants Peter in the Rescue Squad. Further tensions arise when Kelly sees Matt with Heather and assumes he is sleeping with her. Kelly agrees to have a baby with Shay, but she cannot afford the artificial insemination, which leads her to a surprising decision. The firehouse gets shot at, and Casey follows a hunch in order to find the culprits. After attending a depressing funeral, Herrmann tries to reconnect with his family. The firehouse has a touching reaction to a tragedy in the neighborhood.
Casey is angry that Mills has been spending a lot of time with the Squad members and neglecting his Truck duties, but Peter believes Matt might be jealous on him and Gabby. While Herrmann is away hunting, his wife Cindy has a pregnancy complication. Shay and Severide have their first big fight as future parents. Tara, the new paramedic candidate, starts shadowing Shay and Dawson, but she doesn't seem to have what it takes for the job. She does however have a shocking surprise for Severide. Someone from Casey's past makes a comeback.
Severide has to face the consequences of Tara's accusations and the firehouse is ordered to attend a sexual harassment sensitivity seminar. Mills does a great job rescuing a man from an overturned tanker, which raises Hadley's envy. Shay and Dawson need to get past a poisonous snake in order to reach its victim. Matt and Hallie reunite, only to find out that their old nemesis Voight has been released from prison.
Severide decides to look into Tara's past to find evidence that would help him fight the criminal charges she filed against him. Peter asks Gabby to move in with him, but she feels burdened by the secret she's been keeping about his mother. A little girl with a special connection to the firehouse lights everyone's spirits up. The calls of the day include a collapsed apartment building, a car accident and a lightning victim. By the end of the shift, a personal tragedy hits one of the team members.
In the wake of Hallie's death, Casey must join forces with Sergeant Voight and his team in order to track down her killer, even though it means putting his own life in danger. Peter is still shaken after Gabby's confession and that might hurt their relationship. Leslie is very excited as she's about to get inseminated. Also, while preparing for the grand opening of Molly's, Otis convinces his partners to let him hire his Russian cousin as a waitress.
The team faces a hell of a ride when a small prison fire turns into a much more dangerous situation. Meanwhile, Cindy Herrmann goes into labor, Shay is anxiously waiting for her pregnancy test results and Mills faces a turning point in his love life and his career.
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.
Boden forces members of Firehouse 51 to pull themselves back together in the aftermath of a harrowing fire explosion. While Severide goes missing for one week too many, Casey works to track down his whereabouts. Meanwhile, Newhouse brings some unexpected news regarding one of Mills' relatives while Herrmann and Otis make some new goals regarding Molly's.
Lieutenant Severide returns to Firehouse 51, but he is clearly not his usual self. Dawson counts down the weeks until she gets started as a candidate at the Austin Firehouse. Meanwhile, Mills learns more about his father's family and Herrmann asks the potential Molly investors to come up with new ideas to turn the business around.
Lieutenant Casey (Jesse Spencer) deals with the fallout of his sister Christie's (guest star Nicole Forester) impending divorce. Meanwhile, Dawson (Monica Raymund) and Mills (Charlie Barnett) settle into their new roles at Station 51. Elsewhere, Brett (Kara Kilmer) can't decide if she wants to leave Chicago and the Molly's crew still can't figure out how to get the food truck started.
Casey faces his corrupt brother-in-law and Brett goes above and beyond to help a mother in need. Meanwhile, Mills get an education on unlicensed private investigation and Dawson begins training with Herrmann.
A house fire puts a couple in danger; Dawson and Casey are pushed further apart by an unsettling surprise; the Chicago Holiday Fest gives Molly's II a chance to shine; the Chicago FD Chaplain hopes to help out a local soup kitchen with "fill the boot" donations.
The firehouse receives unsettling news when two of their own come up missing following a routine call, prompting members of Chicago P.D. to lead the search. Meanwhile, Casey and Dawson have a hard time figuring how to juggle their personal and professional lives. Elsewhere, Chief Boden and Donna struggle with news that their newborn has potential complications and they receive a surprise out-of-town visitor
Severide and Dawson discover startling evidence found at a storage unit fire that appears connected to the fire that took Shay's life. Meanwhile, the firehouse bands together when Chaplain Orlovsky is the victim of a bad car accident.
An ice storm hits, forcing a citywide lockdown. Mills and Brett are left stranded in the elements while searching for a teen, and the firehouse members babysit a newborn. Elsewhere, Severide receives a job offer, and Chief Boden clashes with his father over his treatment.
Interim Chief Pat Pridgen (guest star Matthew Del Negro) is brought over to temporarily fill in for Boden (Eamonn Walker), who is left to tend to his personal affairs. When tension is sparked as the result of his derisive leadership, the absence of Chief Boden (Eamonn Walker) becomes all too apparent. Meanwhile, Lieutenant Severide (Taylor Kinney) must deal with a most unwelcome addition to his squad, Brett (Kara Killmer) gets closer to a girl she previously rescued and Casey (Jesse Spencer) starts seeing a new woman, Beth (guest star Bree Williamson), but interesting complications quickly unfold.
Severide's old friend arrives, hoping for a second chance with the Chicago Fire Department. Meanwhile, Mills tries to regain his active squad status, Mouch confronts his fear about meeting his child, and Brett and Dawson set out to have a big night out.
Mills tries to save a driver who's been seriously injured in a car accident. Meanwhile, Casey has doubts about the owner of a remodeled strip club and Hermann, Otis and Cruz prepare for the peewee hockey championship.
An apartment fire connected to a case of rape and attempted murder resembles an unsolved case in New York, so Sgt. Benson of Special Victims Unit comes to Chicago to help Intelligence with the investigation.
At Sgt. Voight's urging, a determined Lt. Casey agrees to go undercover in an effort to provide proof of Jack Nesbitt shady dealings. Meanwhile, Otis and Severide continue to disagree about the integrity of Scott Rice, causing tensions to flare between members of truck and squad. Meanwhile, Herrmann helps out a fellow member of the firehouse.
Casey puts his life on the line and digs deeper into the shady dealings of Jack Nesbitt. With members of truck and squad at odds over Rice actions in the field, Chief Boden is left to figure out how to create unity in a divided house, while Severide comes to question his own judgment. A dangerous warehouse blaze quickly gets out of control and threatens members of firehouse 51, prompting Boden and Cruz to risk everything to save their own. Elsewhere, Dawson gets some life-changing news.
Herrmann goes to court to testify against Freddie but when the perpetrators father reaches out to beg forgiveness for his sons malicious attack, a tormented Herrmann is left to figure out what to do. Following the aftermath of the recent tornado, Lt. Casey learns the makeshift shelter housing victims is on the brink of shutting down. At the request of Alderman Colin Becks Casey attends a fundraiser and is thrown into the spotlight, only to quickly discover that his good intentions might not have the impact he was hoping for. Dawson and Brett feel the repercussions after telling Boden about Chilis recent erratic behavior. Meanwhile, Severide helps Agent Alex Ward solve a homemade explosives case and Otis receives a welcome surprise.
Casey and Dawson apply for permanent adoption of Louie. Jeff Clarke gives Severide an interesting proposition. Otis convinces Herrmann to throw a bash celebrating the 100th anniversary of Molly's, but there are complications.
Louie's father throws a wrench into Casey and Dawson's family plans. Severide agrees to a bone marrow donation but a work accident throws everything into flux. Casey and Dawson try to find harmony at home. Meanwhile, Otis and Mouch decide to film a PSA encouraging people to join the Chicago Fire Department but hit a creative wall in the process.
Dawson tries to keep her emotions in check during an ambo run involving a pregnant teenager, while Casey is forced to make a split-second decision regarding two victims in need of assistance and deal with the repercussions.
When similar car accidents uncover the fact that someone may be targeting innocent people, a determined Dawson takes matters into her own hands to help push things along, meanwhile Casey tends to his Alderman's duties.
Lt. Casey butts heads with the new chief who fills in for Boden at House 51; Mullins has an unexpected surprise for Casey when he makes a risky move to stop a man from jumping off the building; Brett learns information about a friend.
While running a secret errand, Dawson finds herself trapped in a collapsed parking structure; pressure mounts on Casey as he begins taking on additional duties; Kidd grows increasingly skeptical of Hope.
Casey and Severide find themselves at odds after Casey argues with him over the best way to save a teenager entangled in barbed wire. When Casey looks to Boden for help smoothing out the situation, he comes to the realization that he will have to fix it himself. Elsewhere, Otis tries to convince Casey to participate in the beta test for an expensive piece of new firefighting equipment imported from Japan. Meanwhile, Kidd and Hope come to blows over a payroll issue and Brett goes on a date with a doctor she meets during an ambo call.
Kidd is surprised to discover she is being transferred out of the firehouse; Severide and Casey are suspicious and investigate; Otis and Herrmann discuss taking over a rundown bar; Dawson's frustration with her father reaches a boiling point.
Brett attempts to make a lifesaving decision in the field to someone near and dear to the firehouse family. In an effort to impress Lily, Otis scrambles to get everything together for the grand opening of Molly's North. Meanwhile, Boden becomes emotional following the rescue of a famous blues player from a burning apartment building and Dawson struggles to come to terms with how she has been dealing with her father.
After saving a young girl, Dawson is forced to make a tough decision when she finds out the girl's father is addicted to painkillers. Herrmann loses his cool and gets into an altercation with a police officer after responding to a call. Otis and Cruz are on a mission to find out who Brett is dating. Meanwhile, Boden is skeptical when Donna's brother Julian unexpectedly comes to town.
Dawson and Casey struggle to communicate; Brett and Kidd compete for the affections of a hazmat officer; Otis, Herrmann and Mouch search for the source of a stench that's making life difficult at Firehouse 51.
Dawson and Casey do everything they can to locate Bria's whereabouts after discovering important new information. Lt. Severide reunites with Chief Grissom, and old family friend. Meanwhile, Cruz enlists the help of Brett and Mouch to create a new tool and Kidd and Zach go on a date.
Casey and Severide disagree on the best course of action following a time-sensitive rescue; Herrmann tries to entertain his daughter on "bring your kid to work day"; Dawson joins Brett on a spa getaway; Kidd's social life gets a boost.
Boden has a lapse in judgment in the aftermath of rescuing a young boy. Kidd struggles to win the approval of Severide's mom after a surprise visit and Otis takes on new responsibilities at the firehouse.
Severide is surprised when Rene Royce returns to the firehouse; Casey helps Chief Boden in his latest pursuit; Kidd regrets a decision regarding Severide; Herrmann disagrees with Lt. Colan Nino over how to coach their son's basketball team.
Boden's chances for a promotion are met with potential complications, leading him to take matters into his own hands. Dawson and Casey don't see eye to eye on an important decision, while Kidd finds herself struggling to find time with Severide. Brett and Dawson respond to a tough call that quickly turns dangerous.