An arsonist targets Lt. Severide. Meanwhile, Station 51 is under scrutiny by Gail McLeod, a financial consultant for the city who is deciding if any firehouses should be closed. Mouch receives a visit from his Japanese girlfriend, Lt. Casey "celebrates the one-year anniversary of Andy's death, and Shay suspects Severide's paternity.

In the wake of Heather's incident, Lt. Casey is having a hard time handling his newfound responsibilities. Lt. Severide is on edge dreading the next attack from the firehouse's arsonist. Meanwhile, with Renee back from her mother's, Severide knows he has to confront her about his paternity suspicions. Elsewhere, Mouch begins his campaign for union president and Shay and Dawson feel that they need to get out more.

Lieutenant Severide is anxious to implicate the serial arsonist, while Dawson and Shay get a shock on a routine call. Meanwhile, suspicions continue to point to Clarke as the mole inside the firehouse and Molly's falls deeper into the red. Elsewhere, Mouch campaigns for union president, with the aid of Isabella, and Boden butts heads with Gail McLeod.

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.

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.

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 makes 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.

Lt. Casey and Dawson volunteer to help at a charity run at Chicago Medical when a massive explosion sends Chicago into chaos. With one of their own missing in the blast, the firehouse is tested like never before.

The crossover continues on Chicago P.D. S01E12 8:30 PM (II)

With everyone’s support, Dawson 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 has an important matter to discuss with Antonio. Meanwhile, Lt. Severide and the firehouse welcome Rick Newhouse , the latest addition to the squad, Shay gets an uninvited surprise guest and Chief Boden makes a bold move.

The Chicago fire team works seamlessly with Chicago Med personnel to help aid victims of a deadly gas leak, but things quickly take a turn for the worse when the hospital is suddenly forced into quarantine.

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.

The crossover continues on Chicago P.D. S02E20 The Number of Rats (II) and Law & Order: Special Victims Unit S16E20 Daydream Believer (III).

At Sgt. Voight's urging, a determined Lt. Casey agrees to go undercover in an effort to provide proof of Jack Nesbitt's 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.

Lt. Casey puts his life on the line and digs deeper into the shady dealings of Jack Nesbitt. Chief Boden must 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.

Casey is placed in a dangerous situation while working undercover to bring down a trafficking ring being run out of Nesbitt's club. The squad's high turnover rate results in an unwelcome surprise for Severide. Dawson recognizes that her life is about to change. A new candidate makes an unusual first impression. Residents band together to protest a drug den in their neighborhood.

The squad members come together to support one of their own. Herrmann tries to figure out how to reopen Molly's after it gets shut down. Severide digs deep into the arson investigation.

Boden believes Maddox is behind Serena's accusations. Severide reaches out to Jamie, who's Maddox's lawyer, in an attempt to help. Patterson questions whether Boden can remain chief. Brett and Chili suspect that a man passed out in a garden is connected to a previous call. Otis has problems with his social calendar.

Patterson fills in for Boden, who's trying to clear his name. Severide learns where Serena may be hiding. Herrmann and Otis give Freddie a job that keeps him close by. Jimmy and Chili draw more attention then either bargained for.

A tornado threatens Chicago. Chili makes a major mistake, which causes Brett to report her to Boden. Otis asks Dawson to help him solve his women troubles. Severide assists a Department of Homeland Security agent.

The team responds to a mass shooting; Casey investigates the missing money from the fund-raiser. Jimmy agrees to represent the firehouse in a boxing match against the Chicago PD's 21st District. Chili's behavior continues to be an issue for Brett.

Severide confronts Chili about her erratic behavior. Members of the firehouse rally around Casey, who they think would make a great candidate for alderman. Jimmy squares off against Antonio in the first annual "Battle of the Badges" boxing match.

Sylvie witnesses a murder and is threatened by the shooter not to go to the police. Firehouse 51 jumps into action when a fire breaks out at a restaurant and traps several people inside a vault. Mouch starts to get cold feet.

Casey steps up to help a teenager being bullied by a gang; Severide bonds with a detective’s son after her life is threatened; and Kidd and Herrmann go head-to-head in a test of bar knowledge.

The team responds to a building collapse that's trapped more than a dozen people. Dawson's quest to foster Louie is aided by a familiar face. Otis, who's on medical leave, meets his temporary replacement. Severide and Kidd continue to see each other. Casey is at odds with Antonio.

Severide and Stella search for Grant, who's AWOL from Chicago Med. Dawson questions her career path. Casey's relationship with his political consultant cools. Borrelli's anger at Boden over his brother's death boils over. Mouch and Brett partner on a new venture.

Casey seeks help with a personal matter from Susan Weller. A rich party guy wants Severide to travel with him. Stella tries to help a sick street kid. Otis and Herrmann share their concerns about Molly's lack of customers.

While responding to a call in the field, Dawson accidentally hits a pedestrian who stepped in front of the ambulance, and is left to deal with the repercussions. Lt. Casey and Lt. Severide disagree and continue to investigate an arson case while Chief Boden is left to decide whether to attend an important function in New York. Elsewhere, in hopes of preparing him for a possible promotion, Lt. Casey puts Herrmann at the helm for a shift so he can discover firsthand what his superiors deal with.

It's a family reunion when Dawson and Antonio's mother and father come to Chicago for their big anniversary party, but things quickly turn south. When a deep secret comes to the surface involving his stepson James, Chief Boden decides to take matters into his own hands. Meanwhile, Casey tries to save a young boy during a harrowing call to a warehouse and Otis and Kidd become competitive at the mud-hundred race.

Lt. Casey and Dawson apply for permanent adoption of Louie, but quickly discover a hurdle. Firefighter-turned-medical student Jeff Clarke approaches Lt. Severide with an interesting proposition. With hopes of reinvigorating business at the bar, Otis convinces a skeptical Herrmann to throw a bash in celebration of the milestone 100th anniversary of Molly's, but not without complications.

The team is on high alert when a previous incident during a fire call leaves a dangerous man on the loose with a vendetta to target Lt. Casey and Firehouse 51, and prompts CPD to step in. Dennis Mack, a buddy firefighter of Severide's father, comes to town to shadow the squad but may have ulterior motives. Meanwhile, Brett and Antonio's relationship hits some bumps in the road when his ex-wife Laura surfaces and Casey has a present for Dawson.

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 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.

While working to track down a bombing suspect, Voight and Antonio meet with Chief Boden, who unwillingly agrees to let Dawson and Brett go undercover. As the investigation continues, Boden, Casey and Severide lend their skilled expertise in the investigation. Elsewhere, Kidd and Zach's relationship hits a bump and Cruz has a hard time expressing his true feelings for Brett. Meanwhile, Herrmann and Connie are forced to come up with an alternative solution when two birthday parties are booked on the same day at the firehouse.

The crossover starts on Chicago Fire S05E016 Profiles (I).

After responding to a car accident, Casey and Dawson become skeptical when a domineering husband continues to answer for his injured wife. Cruz becomes frustrated with Herrmann and Mouch when he discovers they have contacted people regarding his "Slamigan" invention without his knowledge. Kidd uncovers something meaningful and important to Severide while Brett discovers some potentially unsettling news.

In response to a call involving a residential fire, Otis and Kidd's lives are suddenly put in jeopardy when gunfire goes off inside the house. Dawson comforts Brett during an especially trying time. Meanwhile, Casey begins to notice that romance might be going on within the firehouse.

After responding to a residential fire at a property belonging to a Mexican drug cartel, Casey is skeptical of Cordova after a hefty amount of money was found missing from the crime scene. Elsewhere, Kidd makes a big decision.

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