Shay and Dawson roll into the firehouse with pumpkins and huge bags of candy in hand, prepping the firehouse for the upcoming Halloween, Chief Boden's favorite holiday. When Mills is frustrated by the lack of spices in the firehouse, Dawson puts a hand on his shoulder and tells him she keeps coriander, cumin and bay leaves in the back cupboard. He stares at her longingly as she walks away. The bells go off, rousing the lounging firemen. The truck speeds towards an abandoned warehouse that's on fire. Noticing the door's been pried open, Severide suspects there are squatters inside. The men work quickly to evacuate as many homeless people as they can, but the Chief, watching the black smoke rise, predicts an explosion and orders all his men out. Mills, following the Chief's orders, is forced to leave a homeless man still sleeping in the burning building. Seconds later, the top of the building flashes and explodes. Mills watches, disturbed that he couldn't do more.
The following morning, Herrman steps directly into the mayhem that is his family's kitchen. His three kids are boisterously running around dressed in their Halloween costumes as his wife, Cindy, prepares lunches. She hands him the morning paper, the headline of which reads, "Homeless Man Dies in Warehouse Fire" and Herrman's face immediately darkens. As he heads out the door to go to work, his oldest son, Luke, stops him. What if he gets hurt again? "Then I'll get better again," Herrmann assures him with a smile. "Us Herrmanns are tough bastards." At the firehouse, Mills questions Casey about following the Chief's orders at a scene. He's still tormented over leaving the homeless man in the building. After all, he was this close to grabbing him, but Casey tells him not to beat himself up over it. In the locker room, Severide's shoulder sends a searing pain down his arm. Vargas notices and inquires whether Severide was hurt at the scene, but Severide shuts him down. No need for people to start asking questions.
In the kitchen, Cruz, Otis and Mouch discuss the fact that Casey's testifying against Detective Voight's son. The guys are worried about Casey; Voight's not a guy to be messed with. Herrmann enters, still pissed at the obnoxious newspaper headline. Why didn't they write about the three men the firefighters did manage to save? Chief Boden officially announces Jose Vargas' move from Truck to Squad, and the guys react halfheartedly while Casey respectfully shakes his hand. Just then, Nicki alerts Casey that there's something wrong with his car. Casey, Cruz and Herrmann run outside to check it out. The wheels on the truck have been popped, the windows shattered on the drivers seat, and Casey's gym bag has been stolen. Cruz thinks it was probably some punks going wild on Halloween, but Casey suspects otherwise. He decides to contact the police. Inside the firehouse, the alarm goes off as the men are called to a house fire.
Arriving at the scene, Severide sees that the fire's already been put out. Talking to Mrs. Grady, the elderly woman who lives in the house, Severide recalls that they were just at her house two weeks ago, putting out a fire in her car. Mrs.Grady sadly mumbles something about bad luck, but Severide, noticing some sketchy looking teenagers hanging out nearby, has his own suspicions. Two fires in two weeks isn't just bad luck. At the firehouse, the crew is seated around the TV when Chief Boden stumbles upon a news channel interviewing the brother of the deceased homeless man. The brother, upset with the firefighters' lack of commitment, shows cellphone footage from the scene that recorded Boden not letting Mills go back into the fire for the man. An awkward silence permeates the firehouse as Boden shuts off the TV. Later, Mills apologizes to Boden for overstepping his boundaries at the scene, but Boden waves his apology away. That's exactly the attitude he wants from his men. He advises Mills to ignore the bad press.
As Shay and Dawson set out candy in front of the firehouse, they run into Hallie. When Dawson compliments Hallie's shoes, it's revealed that both women are runners who compete in 10Ks. The unacknowledged competition thickens, and the tension is not unnoticed by Shay, who sends Hallie away to Casey's quarters. Casey's surprised to see his fiancee, but it turns out to be a pleasant surprise as Hallie pulls the shades, locks the door and slowly unzips her top. Meanwhile the Chief receives a visit from Sondra Sherman, an attorney with the City's office. She questions him about the warehouse fire, warning him that Marc Thorne, the victim's brother, has concerns about the way the fire was handled and that he may be coming after the Chief and the City of Chicago. Sherman assures the Chief that the City is on his side, but the Chief sends her on her way.
Back at Mrs. Grady's, Severide and a friend of his, Officer Hiller, question her about the two fires. She repeats that they were just accidents and shuts the door on them. Officer Hiller buys her explanation, but Severide thinks that someone in the neighborhood is after her. At the firehouse, Attorney Sherman is back, asking the Chief to have a sit down with Thorne to smooth things over. Sometimes a simple conversation can avert a major lawsuit, but the Chief refuses to back down. He's done nothing wrong, and neither have any of his men. He has nothing to apologize for, even if his job is on the line. In the laundry room, Nicki asks Shay for a key to her apartment. She feels that her father coming to yell at Severide may have pushed him away, and she wants to set up candles and champagne as a surprise for Severide. Shay icily tells Nicki that her dad may not be the problem so much as her fiance and denies her the key.
Shay and Dawson are called in to a baby shower to help a caterer with a nasty cut, but when the women are asked to take a look at the mother-to-be, they're both stunned to see that it's Clarice Schwartz. Back when she was known as Clare and also a lesbian, she was Shay's girlfriend. In the ambulance, it's clear that there are still sparks between the two women, who can't keep their eyes off each other even though Clare's husband is seated right next to them. At the firehouse, Mills' sister stops by to bring the guys food. Sparks fly between her and Severide as he helps her with the bags, but she's out the door so quick it's as if she was never there.
A game of pickup basketball is interrupted at the firehouse when Marc Thorne, followed by a friend with a video camera, requests to speak to Chief Boden. The Chief walks up to Thorne and shakes his hand, telling him he's sorry for his loss. This isn't enough for Thorne, and when he continues to question Boden's motives, Herrmann steps in, unable to hold his tongue. Why is Marc only so concerned about his brother after his death? Where was Marc when his brother was trying to keep warm in a warehouse? Boden and the rest of them are firefighters. They save people for a living, and they tried to save his brother; but Chief Boden made the call he had to make. "Just be glad you never have to do that," Herrmann tells a stunned Thorne. The rest of the firehouse watches on in admiration.
Turns out the whole staff remembers Clarice, and none of them were too fond of her. When Dawson tells everyone Clarice is now married and with child, Otis leaps up, swearing that he'd always called Clarice as having one foot in, and one foot out! Shay is not amused. The truck is called to a hopping Halloween block party. As Shay and Dawson take care of the seizing man, a drunken frat boy dressed as a firefighter starts causing trouble. "Just don't tell them you're homeless... they won't help you!" he mouths off. Herrmann's unable to keep his cool and shoves the guy, but Casey intervenes before the situation can escalate. Sherman is still lurking the hallways and this time she's got bad news for the Chief. The M.E.'s report came in, and Jonathan Thorne died from injuries sustained during the explosion. The department is now putting together a committee. The Chief walks away slowly and shuts himself in his office, pacing.
Back from the Halloween banger, Casey steps outside to see Detective Voight waiting for him, donning a leather jacket and leaning against an unmarked police car. As an apology for his behavior, Voight made Casey's car case a priority and found the guy who did it. Casey's apprehensive, but Voight throws Casey's gym bag in his hands. When Casey unzips the bag and takes out a hug wad of cash, he looks up at Voight, uneasy. "This isn't mine." "Guess the kid stashed it in there," replies Voight with a knowing smile. He tells Casey that there's one simple honest solution to their little tussle. All Casey has to do is change the report about Voight's son drunk driving, and Voight will leave Casey alone. Casey sets down the cash on the hood of the car and walks away, Voight staring menacingly after him.
When Casey tells Dawson about Voight's bribe, Dawson's horrified and suggests that they tell her brother, but Casey just wants to testify and let the courts handle it. He doesn't want to tell Hallie either for fear of worrying her. At their apartment, Shay and Severide are drinking the night away. Shay's slightly slurring her way through a vent about how different Clare is now, all rich and fancy with a floor to ceiling wine rack. We learn that Clare and Shay dated for three years: not a throwaway relationship by any means, and Shay has a right to be so heartbroken. The roommates are interrupted when Nicki knocks on the door and heads up to Severide's bedroom. She's expecting a good night, but instead Severide casually hands her a beer and tells her he was engaged once too. Moments later, we see Nicki exit the apartment, tears in her eyes. The next morning Sondra informs the Chief that a settlement's in the works, and Thorne has dropped all the charges.
For the third time, the guys are called to Mrs. Grady's apartment where a Molotov cocktail thrown through the window has started a fire. Poor Mrs. Grady is on a stretcher, her eyes alarmed as she breathes through an oxygen mask. Severide promises he won't go to the police, but she's got to tell him what's going on. Later, we follow Severide up a flight of stairs to a dingy, smoky apartment. He knocks on the door of two teenagers, apparently drug dealers whom Mrs. Grady once called the cops on. Severide threatens that if one more ember goes anywhere near her property, he'll break their kneecaps and drag them to the police station. Severide's tone and the fire blazing in his eyes mean business, and the two punks know it.
The following morning, the Chief is somber as he announces Nicki has quit her job. She's broken off her engagement and left to go to Europe for a while, so they need to refill the position. Dawson walks in on Shay dialing Clarice's number and sternly stops her. It's not like she can forget peeling Shay off the floor after the woman broke her heart. Shay knows Dawson's right, but even so, her heart aches for a lost love. In his office, the Chief sits Mills down and tells him that at one point in his career, he also thought he had a minute to save a victim. He and his best buddy ran into the building but didn't see the fire trapped in the ceiling. They ended up losing the victim, and Boden lost his best friend. To this day, the scar on his back reminds him every single day the price you pay when you try to beat the clock. It's his job to make sure his men never have to get those kinds of reminders. "You're going to make one hell of a firefighter," the Chief gently tells Mills, "Just like your dad was." Minutes later, we follow Mills to the Chicago Fire Academy, where he stares at the memorial for fallen firefighters. Directly across from him is the badge for Henry Mills, died 1992.
Elsewhere in Chicago, Severide and Shay are strolling down a street full of bars and shops. With a tear rolling down her cheek, Shay breaks down and admits she really thought Clare was the one. Severide kisses her gently on the forehead and puts his arm around her, steering her down the street. At the firehouse, Casey gets an emergency call and rushes to Hallie. In the lot of the hospital, he sees her car's been broken into just like his was: tires slashed and windows shattered. Casey says nothing, but his eyes are wide and his breathing heavy. A chill goes down his spine as he realizes he and his loved ones are being targeted.