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.

Lt. Casey struggles to get Chief Boden to sign off on an energetic new recruit. Against her better judgment, Foster extends an olive branch to her irritating new medic. Otis inspires Herrmann to seek new partners at Molly’s. Brett realizes life in Fowlerton will take some getting used to.

Brett and Foster question the suspicious circumstances surrounding a brutal attack at a juvenile detention center, which leaves them searching for the truth. A convoluted new technology installed inside Firehouse 51 tests everybody’s patience. Kidd gets chosen to represent the district at a leadership conference.

A rare but 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. Following a fire at a local university that ties into the outbreak, Severide has suspicions that something bigger is happening.

The crossover continues on Chicago Med S05E04 Infection, Part II (II) and Chicago P.D. S07S04 Infection, Part III (III).

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 everyone in the firehouse informed by starting a newsletter, but things quickly get out of hand. 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. 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.

The crossover continues on Chicago P.D. S07E15 Burden of Truth (II).

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.

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 rescue 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 is 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.

A fire at a homeless encampment leaves Severide and Casey searching for answers. Cruz is shaken up after a close call. Ritter lends a helping hand to a victim.

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 rescue 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.

Casey makes a life-altering decision. Gallo, Ritter and Violet agree to an interview and photo shoot. Brett and Mouch launch the paramedicine 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.

Gallo clashes with the new lieutenant temporarily filling in for Casey. Severide closes in on a dangerous and deadly arsonist.

Severide and Herrmann clash over office space. Boden looks at Pelham’s past as he considers making him permanent. Gallo’s resentment of Pelham comes to a head. Brett and Ritter force Violet to confront her true feelings for Gallo.

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

Stella Kidd returns to Firehouse 51. The team must work together to put out a potassium fire in a tunnel. After that incident, Ritter begins to worry about a young cop who witnessed the fiery death of a truck driver.

On a call with Station 37, a firefighter is struck by a power line and decides to lash out after her injury. Brett is visited by Scott and Amelia. Violet gets a surprise envelope. The rest of 51 enters a contest.

Boden, Kidd and Severide work together to protect one of their own. At the Fire Academy, Herrmann meets an inspiring young man. Talk of the annual CFD Gala dominates the firehouse.

Severide and Seager team up to investigate a fire at the home of a troubled young woman. Pelham moves into 51's rumored cursed office. Kylie assists Kidd with Girls on Fire.

Chief Hawkins goes above and beyond to help Brett and Violet with a problem. Kidd pursues an open lieutenant position. A blast from the past asks Mouch and Herrmann for a favor.

Following an injury in the aftermath of an industrial fire, Severide and Seager work together to investigate an anonymous tip. Kidd searches for the right person to fill the opening on Truck 81.

Cruz forms a bond with a young immigrant boy he meets while fighting an apartment fire. Squad makes plans to prank the newest member of their team.

Severide and Kidd work with CPD regarding a suspicious car wreck. Hawkins and Violet's relationship is in jeopardy. Chloe and Cruz adjust to a new family dynamic.

Firehouse 51 must band together when one of their own is taken hostage.

Firehouse 51 tackles a fire caused by a dropped jet engine, and one of their own is accused of a theft related to the incident. Kidd and Boden disapprove of Kylie's potential new love interest.

A family friend asks Herrmann for some advice on opening a bar. Tensions run high between Emma and Violet. Kidd struggles to keep her team together.

Mouch and Ritter work together to solve a murder mystery. Severide and Cruz tackle a food truck fire. Gallo goes to see Hawkins about Violet.

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.