A month after a devastating loss, firefighters of the Chicago firehouse 51 fight to work past it and continue to serve the city.

An injury sidelines Herrmann. Severide carries out a victims last wish after failing to save him. Casey wants to restart things with Hallie. The fire crew are having issues with a goat being on their insignia.

Casey is pressured into recanting a statement when he learns a drunk driver is the son of a veteran CPD detective. Severide learns the severity of his injuries. Mills wants out of the family business to pursue firefighting.

Boden faces backlash after his decision to pull his team from a burning warehouse. Voight steps up his threats against Casey. Severide suspects arson threats against an elderly lady. Leslie has an encounter with an old flame.

Kelly seeks help from his ex in acquiring painkillers. Herrmann gets stuck in a pyramid marketing scheme. The feud between Casey and Detective Voight becomes personal.

Casey reaches a boiling point with Detective Voight and gets an angel to help take him down. Dawson faces off with the suspension board.

It's Thanksgiving and Boden order's a drug test for the 51, putting Severide in a tough position. Cruz's brother is injured in a gang shooting. Otis starts a podcast. Leslie's ex-girlfriend visits the firehouse.

Mills considers leaving the 51 after encountering the remains of a victim. Leslie is confronted by Clarice's husband. Severide develops an addiction to painkillers. Dawson suspects a mother poisoning her daughter.

An injury on the job forces Vargas to retire. Cruz seeks to pull his brother from a gang and the price is high. Severide starts a relationship with a woman he saved on a job.

The 51 crew is under investigation when a woman accuses the firemen of stealing a diamond necklace from her home. Cruz makes a risky move to pull Leon out of a gang. Things get serious with Kelly and Renée.

Casey sees his mom in prison.

Dawson is stuck in a love triangle between Casey and Mills. Casey is asked to speak at his mother's upcoming parole hearing. Severide comes clean to Boden about his arm injury.

Kelly considers moving to Madrid with Renée and learns the risks of surgery. Matt speaks for his mother at the parole hearing. Boden races against the clock to save Ernie. Leslie offers Clarice a place to stay.

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 the wake of a shooting that placed her brother in the ER, Gabriela seeks help from an old enemy. Herrmann learns his silent partner is a thug. Leslie and Clarice face a custody lawsuit with Daniel. Casey seeks closure.

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.

Shay decides she wants to have a baby. Gabby, Herrmann and Otis finally name their bar. Kelly's father visits Firehouse 51. Boden hosts a Fire Academy Gala. The truth about the death of Mills' father is revealed.

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.

Kelly pushes to get Peter on the Rescue Squad, while chewing out Casey for being around Darden's widow. A tragedy strikes the fire crew. There is a shooting at the firehouse. Herrmann tries to reconnect with his family.

Mills focusing on making squad causes a rift in the 51. Herrmann's wife comes to the firehouse and experiences complications. Shay and Dawson are having issues with the new ambulance candidate.

Severide faces a bizarre accusation and the 51 is ordered to attend a sexual harassment sensitivity seminar. Matt and Hallie reunite. Voight is released from prison and reinstated. Mills sparks Hadley's envy.

Severide digs into Tara's past to fight a case against him and learns this wasn't her first rodeo. Peter asks Gabby to move in with him. The 51 meets a young girl who Boden knew from a past. A personal tragedy hits Casey.

Casey must set aside his differences with Voight to find Hallie's killer. Peter is reeling from the truth about his father's death. Leslie prepares for insemination. Otis hires his Russian cousin as a waitress as Molly's is set to open.

The 51 are sent to a prison to do a job and all hell breaks loose. Cindy goes into labor. Shay learns the results of her pregnancy. Mills learns about his chances to make squad. A familiar face returns to Severide's life.

Boden learns his firehouse is in danger of getting shut down. Severide is being targeted by an arsonist. Mouch brings his new girlfriend to the firehouse. Molly's is facing a competition from a new sports bar down the street.

The threat of an arsonist with a vendetta against the firehouse looms and Casey struggles with the repercussions of Heather Darden's accident.

Severide is convinced he knows the arsonist's identity.

Internal issues threaten to derail Engine Company 51.

The future is uncertain for more than just Boden and Firehouse 51.

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.

McLeod continues to pressure Chief Boden, threatening to close Station 51, since he failed to retire as planned. "Mouch" steps up to pressure the union leader to preserve the station.

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.

An explosion at a hospital where Casey and Dawson are volunteering for a charity run sends Chicago into chaos.

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.

A fire at a boarding school shakes up Lt. Severide; Lt. Casey tries to help Dawson; Mills looks into his father's past.

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.

Tensions run high when trucks from two firehouses collide and fingers are pointed towards Cruz for his driving.

Dawson tries to strike a balance with Casey during her first day as a candidate. Meanwhile, Mills ponders an uncertain future; Severide faces his demons; and a city inspector visits Molly's.

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.

During a house fire, Firehouse 51 rescues the owner from the cellar clutching a suspicious box, leading Lt. Severide to bring in Sergeant Voight and Detective Lindsey for further investigation.

The members of the firehouse spring into action when a helicopter explodes over a populated area.

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 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.

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.

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.

The interim chief makes a tactical error during an apartment fire, stirring up tensions and putting careers in jeopardy.

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.

Herrman 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 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.

Casey finds himself in dangerous territory at the center of an undercover operation to bring down a trafficking ring out of Nesbitt's strip club.

Internal Affairs investigates Firehouse 51 following a complicated call to a fire.

Boden's job is on the line as the crew of Firehouse 51 continues to search for evidence that could clear him of any wrongdoing.

A member of Firehouse 51 requires the support of the whole team to recover from a near disaster.

Boden offers to host a wedding at the firehouse after a fire ruins the ceremony, but Chief Riddle is against it and his political aspirations cause friction among the firefighters.

Severide and Patterson's differences reach a boiling point, while a visitor from Cruz's past asks for a favor.

Boden finds himself in the middle of a fiasco concerning a female neighbor he believes is setting him up.

Patterson confronts Boden about his ability to lead the firehouse.

Clues to Serena's possible whereabouts are uncovered, while Captain Patterson has news for everyone.

While a member of Firehouse 51 falls victim to a near-fatal stabbing, the other firefighters rescue a woman who attempted to commit suicide.

The city of Chicago braces for a tornado.

A tormented Herrmann is forced to make a difficult decision and Casey does his best to keep a shelter open that's housing recent tornado victims.

Mysterious threats begin to emerge throughout Chicago and the situation gets worse when news of a mass shooting brings Firehouse 51 into a dangerous scene.

Severide confronts Chili about her behavior, while Jimmy faces Antonio in the first annual "Battle of the Badges".

Severide and Cruz take matters into their own hands when Firehouse 51 responds to a suspicious call from a neighboring firehouse.

A citywide propaganda attack against Casey's run for alderman makes him reconsider his candidacy.

Severide and Cruz discover the remains of a case that may be connected to a case Severide worked on years ago.

Sylvie is threatened when she witnesses a murder.

Casey tries to use his political influence when a high school student is almost killed by a street gang.

Severide watches over Detective Holloway's son while she testifies in court as part of an undercover operation, but he's left to deal with the situation due to an unexpected turn of events.

Dawson risks her life to save a young boy from an apartment fire.

Firehouse 51 heads to the scene of a building collapse where dozens of lives are on the line.

Dawson hopes to foster Louie while a dangerous structure fire puts a member of Firehouse 51 in a dangerous situation.

Severide and Stella are on the lookout for her unstable ex.

Members of 51 end up in a dangerous situation while responding to an auto accident and Stella must make a serious decision about her ex.

Casey gets help from Susan Weller for an urgent personal matter; Severide is given an opportunity to travel with Travis Brenner; Stella saves a street kid from a tunnel fire.

Casey is forced to take extreme measures when a forklift accidentally pierces a tank of acid, causing it to spill and putting a father and daughter in danger.

Casey and Severide disagree on a potential arson case when the squad fails to save a woman from her burning house.

Dawson hits a pedestrian while responding to a call. Casey and Severide continue to investigate an arson case while Chief Boden is in New York to attend an important function.

Gabriela and Antonio's parents come to Chicago for their anniversary, while Chief Boden discovers a secret about his stepson.

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.

Dawson and Casey meet Louie's biological father. In other events, Severide falls back into old habits as he tries to help Anna with a bone marrow procedure, and Brett opens up to Dawson.

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.

A dangerous man is after Casey for an incident during a fire call.

A superior comes after Boden for making a split-second decision in an accident that overrides him.

Members of Firehouse 51 are split up and reassigned to various houses in Chicago by Chief Anderson.

Firehouse 51 responds to the scene of a blaze that puts many lives in danger, including someone related to a Chicago police officer.

Firehouse 51 is taken over by local gangsters.

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.

Dawson and Brett have a new trainee assigned for their shift; Severide's father pays him an unexpected visit.

Casey is reunited with an old colleague when the squad's rig breaks down in the field.

Casey takes drastic measures to help Kannell.

Cruz faces a possible suspension from the fire department for an off-duty incident.

A dangerous warehouse fire puts truck and squad at risk. Tensions rise for Dawson and Casey as Dawson's father overstays his welcome at their home. Mouch considers retirement.

With most of the squad still trapped in the warehouse fire, Chief Boden makes a risky last-minute decision to save them.

When Boden learns that the school fire in which his wife was trapped was not an accident, he pressures Severide and Casey to find the cause.

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, an 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.

The photographer whose pictures of Casey and Severide during a rescue make the front page of the newspaper chronicles a day-in-the-life story at the Firehouse.

The firefighters help the police track down a bombing suspect.

A domineering husband answers for his injured wife after Casey and Dawson respond to a car accident.

Otis and Kidd respond to a call involving a residential fire only to head into danger when gunfire goes off in the house.

The members of Firehouse 51 come to terms with one of their own being injured and deal with the temporary replacement.

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.

Casey and Severide assist the FBI with an undercover mission; Kidd tries to help Severide come to terms with recent developments.

Casey grows skeptical of Cordova when a large amount of money turns up missing at the property of Mexican drug cartel.

Boden and Severide receive a surprise package after saving a girl from a car accident.

Severide is surprised when Renee Royce returns to the firehouse; Casey helps Chief Boden in his latest pursuit; Kidd regrets a decision regarding Severide; Herrmann disagrees with Lt. Colannino over how to coach their sons' basketball team.

Boden takes a big step in the pursuit of a major career decision. Kidd becomes increasingly distrustful of Renee's motives with Severide. Herrmann has trouble bouncing back after a tragedy.

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.

Casey struggles with his personal life; the firehouse welcomes a new member; Boden clashes with the new assistant deputy commissioner.

A raging fire consumes a 25-story apartment building complex, trapping victims on the top floors.

Boden becomes skeptical of Gorsch's motives; Severide gets involved in a difficult situation following a child's rescue from a car wreck; Foster is tasked with giving Cruz personal advice.

A series of explosions hit Chicago; Herrmann adjusts to his new duties; Kidd is visited by an old friend.

Casey investigates the cause of a trailer park fire; Boden reaches his breaking point; Mouch, Herrmann and Cruz wonder why Molly's isn't living up to expectations.

Gorsch takes over Boden's morning meeting at Firehouse 51 and goes out on calls in his place; Brett and Foster respond to a call about a Halloween prank getting deadly serious.

Severide struggles to process his father's death; Brett thinks a teenage driver in a car accident is hiding something.

Firehouses 51 is called in to battle a structure fire that places everyone in peril.

A car pile-up impacts someone dear to the firehouse family. Brett and Foster encounter a harrowing call while Kidd and Severide find their relationship being tested.

Casey and Naomi escape a deadly fire in his apartment. Brett puts together a team to create a community fire safety presentation but they struggle to make it engaging. Severide and Kidd are at a crossroads.

Foster faces blowback after pointing out a doctor's oversight. Brett helps Casey look for a new apartment. Kidd prepares Tuesday the Dalmatian for the Fire Safety Dog Competition. A serious accusation is leveled against Severide.

When the firehouse is called to a motorcycle crash, Casey and Severide sense that the details don't add up. A rift develops between Mouch and Otis. Brett, Foster and Kidd work to secretly fix a dent in the ambulance bumper.

Cruz leads the charge in getting the firehouse to gear up for the Polar Plunge. Herrmann has a hard time bouncing back after dealing with a tough call. Foster's personal relationships begin to interfere with her job.

Brett, Foster and Kidd take a road trip to Indiana and encounter an accident involving a boys' hockey team that leaves them scrambling and relying on their instincts to save the injured. The rest of Firehouse 51 competes in the annual chili cook-off.

A spate of robberies comes to light after a firehouse lockbox key goes missing. Sergeant Hank Voight suspects a firefighter may be involved, and with Boden's support, he recruits Cruz to go undercover to help sniff out any suspicious activity.

Casey struggles after experiencing a narrow miss on a call. Otis wins a unique sporting opportunity in a raffle. Grissom turns to Severide for assistance when the mayor's office sends a task force to Firehouse 51.

Tensions run high between Casey and Herrmann after the firehouse responds to an apartment complex fire. After discovering something extremely suspicious during the call, Kidd and Severide do some investigating and get CPD on the case.

Severide gets angry at Cruz when he feels his orders were disobeyed in the field. Boden reconnects with an old high school friend during a call to a house fire. Herrmann has issues when one of his favorite knick-knacks from Molly's goes missing.

A horrible storm wreaks havoc on Chicago and impacts Firehouse 51 when the power goes off. A little boy mysteriously shows up at the station and everyone works together to uncover who he belongs to. Foster and Kidd argue about Severide.

Severide and Boden search to uncover whether arson was the cause of a fire at a hair salon. Mouch, Herrmann, Otis and Kidd make a startling discovery while tracking down the missing piercing nozzle from Engine 27.

A serial arsonist cold case is reopened when Lt. Severide finds a connection to a recent salon fire. Firehouse 51 celebrates a retirement party.

Severide and Kidd continue to investigate Benny's old arson case. Unexpected news leads Brett to ponder a big decision. All hell breaks loose.

The mattress factory fire spirals out of control. Truck and squad lay it on the line in hopes of getting the trapped victims out alive.

Casey struggles to get Boden to sign off on an energetic new recruit; Foster extends an olive branch to her irritating new medic; Otis inspires Herrmann to seek new partners at Molly's.

Brett and Foster question the suspicious circumstances surrounding an attack at a juvenile detention center; new technology at Firehouse 51 tests everybody's patience; Kidd is chosen to represent the district at a leadership conference.

A deadly bacteria takes its toll on numerous victims around the city, leaving Chicago's finest first responders to work together alongside the CDC to resolve the dangerous situation; Severide suspects something bigger is happening.

Kidd must prove herself at the National Firefighter Leadership Conference, while the rest of Firehouse 51 is called to two eerily similar car wrecks. Mouch tries to keep the firehouse informed by starting a newsletter. Cruz deals with a heartbreak.

Cruz and Severide suspect foul play when a fire started by an elderly woman turns deadly. Kidd, Foster and Brett create a women's-only lounge. Firehouse 51 celebrates some good news.

Severide must make a tough decision about the future of his career at Firehouse 51. Herrmann deals with the consequences of his temper after a run-in with a Chicago police officer. Cruz is excited to demonstrate the Slamigan at the Firefighting Expo. Commissioner Grissom returns.

Severide begins his assignment at the Office of Fire Investigation and gets off on the wrong foot when, despite his orders, he reopens an old case. When the cause of an apartment fire hits close to home, Herrmann is on a mission to get to the bottom of it. Kidd finds herself burning the candle at both ends.

An unexpected visit throws Casey for a loop. Severide sets out to exonerate a wrongly convicted arsonist. Kidd pays the price for burning the candle at both ends. Cruz goes on a mission to fix one of Otis's old toys.

Members of Firehouse 51 are dismayed to learn their boundaries have been redrawn to overlap with an adjacent station and problems quickly arise. Casey and Gallo hunt a missing piece of equipment. Brett and Foster find themselves at odds. Mouch tries the find the recipient of a mysterious letter he discovers.

A pest control problem forces the 51 team to temporarily bunk with Firehouse 20. All under the same roof, Casey clashes with Capt. Delaney while Foster, Kidd and Brett fear Capt. Leone has it out for them. Boden mulls a procedural overhaul.

A series of false alarms at a private school hinders the firehouse's ability to respond to legitimate emergency calls. Kidd asks for ideas to surprise Severide on his birthday. Cruz and Brett rent out their extra room, but the new tenant is more than they bargained for.

The surprising arrival of a new fire truck brings both joy and chaos to members of Firehouse 51. Boden and Severide are asked to make peace with an old foe for the greater good. Brett receives family news while Foster plans a party with friends.

A series of mysterious gas leaks has members of Firehouse 51 puzzled and spread thin. Brett's conflicted when her birth mother gets serious about tracking her down. Severide misunderstands his role as Cruz's best man. Mouch bites off more than he can chew.

A series of teen Opioid overdoses sees Severide partner with Sean Roman, but begins to suspect there's more to the story than his old friend is telling him. Casey tries to be there for Brett as she considers her birth mother's offer to meet.

Boden is on edge after starting a new fad diet. Casey and Severide disagree on a call. Brett's birth mother shares life-altering news. A familiar face has a proposition for Herrmann.

Things get personal for Casey and Gallo in the aftermath of a suburban house fire involving a mother and her young son. Herrmann campaigns for more respect. Kidd has an idea for giving back to her community.

Lt. Severide teams up with Seager and the OFI when a motel structure fire turns suspicious. Firehouse 51 members become amateur sleuths following a Reddit post involving one of their own. Brett continues to get invested in her birth mother, Julie.

Tension builds when a group of rabble-rousers attempt to lock down the firehouse. Brett is faced with a monumental decision. Cruz readies himself for a big day. Gallo and Ritter attempt to launch Firehouse 51 into the social media age.

When one of 51's own gets injured on a call, Lt. Severide becomes obsessed with helping out. Foster contemplates a big decision. Kidd is concerned for one of her high school trainees.

As Firehouse 51 welcomes a new member to the team, whose presence could provide some complications, Brett's leadership shines during a scary call; Boden sees great potential in Kidd and proposes an idea that could have lasting repercussions.

Brett and Mackey find their lives in peril. Casey and Brett tread in unfamiliar territory. Severide chases a memory while Kidd adeptly solves a firehouse problem. Ritter puts himself in harms way during a harrowing call.

A mishap on the aerial ladder in the midst of a fire leaves Mouch shaken and questioning his abilities. Kidd looks for support from Severide while Casey and Brett discuss their future.

While completing a task assigned by headquarters, Boden makes an unforeseen connection. Gallo's forced to make a surprise rescue to one of their own when the firehouse is called to the site of a construction explosion. Mouch reignites an old feud.

When Firehouse 51 is called to the scene of a dangerous blaze inside a 10-story storage unit, Herrmann and Cruz find themselves trapped inside a freight elevator with all communications cut off.

Gallo makes a split-second decision during a dangerous fire rescue leaving Casey steaming that his direct orders were not obeyed. Kidd feels a strain in her relationship with Severide. Brett and Mackey find themselves searching for answers following a series of suspicious calls.

Casey and Severide investigate a suspicious fire at a homeless encampment. Cruz is shaken by a close call. Ritter bonds with a victim. Sylvie flirts with Grainger.

A call to a familiar location brings back mixed emotions for Severide; Herrmann heads out for a vacation; Casey is not thrilled with his replacement

Mouch, Gallo, Ritter and Mackey report for training. A nasty blow to the head brings Casey unimaginable pain.

A series of suspicious fires sends 51 on a search for the cause. Casey continues down a troubling path. Mouch is looking to make his long-awaited dream come true.

A new recruit with ties to the CFD tests Serveride's patience. Violet receives a mysterious note that sends her and Brett on a hunt for the person who wrote it.

While Mouch makes an incredible save, all eyes are on a mystery man who helped save his neighbor. Casey worries about his future at the CFD.

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.

A fire breaks out at a pet food factory and Casey and Severide help the owner, Pete, get to the bottom of it. The annual garage sale takes place at 51 and everyone is on edge.

Severide and Casey try to find the best fit for Kidd. Ritter, Gallo and Violet help plan an event for Mouch.

The firehouse reacts to some exciting news, a mysterious stranger arrives and a shocking call takes Severide's breath away.

Firehouse 51 deals with the aftermath of the capsized boat rescue. Gallo, Ritter and Violet discuss plans for a side gig.

A video of Casey from the roof 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.

In the show's milestone 200th episode, Casey makes a life-altering decision. Gallo, Ritter and Violet agree to an interview and photo shoot. Brett and Mouch launch the para medicine program. Cruz comes closer to fatherhood.

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.

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.

A familiar person returns to Firehouse 51 to serve with Kidd on a special task force. Tony is close to breaking the CFD's perfect attendance record. Old grudges resurface when Gallo reunites with a family member.

Brett waits for life-changing news; Herrmann encounters a psychic with a grave warning on a call; Kidd finds a new lead on the Homeland Security case.

Casey is forced to take extreme measures when a forklift accidentally pierces a tank of acid, causing it to spill and putting a father and daughter in danger.

In the show's milestone 200th episode, Casey makes a life-altering decision. Gallo, Ritter and Violet agree to an interview and photo shoot. Brett and Mouch launch the para medicine program. Cruz comes closer to fatherhood.

Casey is pressured into recanting a statement when he learns a drunk driver is the son of a veteran CPD detective. Severide learns the severity of his injuries. Mills wants out of the family business to pursue firefighting.

Things get personal for Casey and Gallo in the aftermath of a suburban house fire involving a mother and her young son. Herrmann campaigns for more respect. Kidd has an idea for giving back to her community.

Casey must set aside his differences with Voight to find Hallie's killer. Peter is reeling from the truth about his father's death. Leslie prepares for insemination. Otis hires his Russian cousin as a waitress as Molly's is set to open.

Casey tries to use his political influence when a high school student is almost killed by a street gang.

A dangerous warehouse fire puts truck and squad at risk. Tensions rise for Dawson and Casey as Dawson's father overstays his welcome at their home. Mouch considers retirement.

Severide digs into Tara's past to fight a case against him and learns this wasn't her first rodeo. Peter asks Gabby to move in with him. The 51 meets a young girl who Boden knew from a past. A personal tragedy hits Casey.

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.

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.