It's a drab afternoon on the grey streets of Chicago as two fire trucks race towards a scene. The mood inside the trucks is determined but light, and the crew jokingly jabs at one another as the driver speeds on down the road. Once on the scene, they learn that a victim is still stuck inside the attic. Lieutenant Kelly Severide, head of the rescue squad, heads in first. He's confident, fearless even. Lieutenant Matthew Casey climbs up the ladder alongside Andy Darden, who breaks in a window before he's given instruction to do so. Realizing the conditions are still unstable, Casey yells at Darden to stay out but Darden's already in through the window. Downstairs, Severide realizes that there's no vent. Thick black smoke begins to get sucked upstairs; an explosion in waiting. Severide hollers for everyone to get down but it's too late. Trapped, Darden perishes, engulfed in flames as Casey watches helplessly from the ladder.
A month has passed. Losing one of their own has left a toll on the entire squad, and Casey and Severide, once close friends, are experiencing a painful rift due to the death of their mutual friend. It doesn't go unnoticed; Chief Wallace Boden calls both of them in to discuss the unnecessary animosity between both leaders. At the firehouse, an enthusiastic young man enters. He's Peter Mills, the new candidate who's replacing Darden. Firefighter Cruz gives Mills a quick tour. Elsewhere in Chicago, strong-willed paramedics Leslie Shay and Gabriela Dawson are responding to a shooting that occurred during a drug deal. As they're working on one gunshot victim, the other stumbles out of the closet, hurt but ready to shoot. Gabriela handles the situation forcefully and gets him to drop his gun: although there's terror in her eyes, it's clear that this isn't her first time in a life-or-death situation.
Back at the firehouse, Peter's already on babysitting duty as he lectures a group of kids visiting the station. He explains to them that this firehouse is special because it's got both truck guys and a rescue squad. Proudly, he explains that the rescue squad does it all: they're experts in water rescue and extraction and take on whatever is needed of them. Mills hopes to follow in his fathers' footsteps one day and join them.
An alarm sounds and the firehouse is a flurry of men putting on their gear and loading the truck, calmly but quickly. They race towards a bridge, where a mother and daughter are trapped in a car after a collision. The scene is intense, and the two are responsive but severely hurt. Gabriela assesses the victims as the firefighters remove the doors from the car. Noticing a bent windshield, Mouch believes that the driver was ejected into the water, and the squad immediately sends down two divers. Shadowing Mouch, Mills spots a suit jacket in the car and looks over the crowd watching the scene unfold: everyone is bundled up except one worried looking businessman. Mill goes with his gut and tackles the guy, believing him to be the driver.
At the firehouse, tension escalates over the mistake made back at the scene. It looks like it's truck against squad before Chief Boden interferes, scolding the men for their behavior. He reminds the team that it's been almost a month since Darden's tragic death, and they need to change and move past this together. Moments later, Darden's wife Heather drives up, and Casey hands her Darden's things, cleaned out from his locker earlier that day; 14 years all collected in a single box. She's got two kids in the back seat and can barely hold it together, as hard as she's trying.
Leslie and Severide meet in the hallway, where Leslie secretively hands him a vile. Severide locks himself in a bathroom stall and injects the medicine into his right arm, which seems to be cramping up on him. Outside the firehouse Casey runs into Gabriela, who's obviously had a rough day. She invites him to a bar tomorrow night, but he tells her he and his girlfriend have a date night planned, though he seems a little wary about it. The scene cuts to Chris' house, where he and his family are all packed up in their van and ready to move back in with their in-laws, their house in foreclosure.
Back at Casey's apartment, he's biting into a piece of old pizza when Hallie, his girlfriend, shows up at his door with some fresh food. After some awkward small talk, Hallie places an engagement ring on the empty counter. We learn that Casey's moved out, and their engagement has ended because Casey wants to start a family, while Hallie, who's a full-time hospital resident, isn't ready for one. They're stuck in the worst kind of relationship limbo. Neither of them wants the same thing, but neither of them can bear to move on.
It's a new day the firehouse, and the crew is hustling Mills, telling him to hit on Leslie when, in reality, she's gay. The Chief calls in Leslie and Gabriela and questions them about the young girl at the scene a few days ago: Gabriela had to perform emergency surgery on the way to the hospital and inserted a needle into the girl's heart. Although Gabriela was doing it to save the girl's life, now her job may be on the line. Casey decides to cook Sunday night dinner for the crew, but Severide makes a show out of not eating his food. Casey confronts him outside; Severide is still angry that Casey allowed Burden to enter the scene before it was ready. The sadness and guilt about their friend's death traps both men in a cycle of blame.
Come nighttime, some of the truck crew heads over to the local gym to watch badges fight badges. It's a regular fight club, with Chief Boden fighting a police chief, apparently one that slept with his ex-wife. The rest of the crew is spread across the firehouse, listening in on Otis' account on the walkie-talkies. Another fire alarm interrupts, and the crew speeds off to a house fire down the street.
The fire inside the apartment building is raging, and Casey shouts out directions. Casey and Herman scour all the floors for people still trapped in the building, with Cruz and Mills following suit on the roof. Mills seem to be working well under pressure. The Chief arrives on the scene and warns Casey they've got to go as black smoke begins to bellow out the windows. Casey's on his way with Herman, but the brittle floor collapses and sends them hurtling down to the basement, where the collision is massive.
The squad arrives on the scene and the Chief alerts Severide that Casey and Herman are currently unresponsive. Severide is lowered into the basement and wakes up Casey, but Herman is barely breathing. They manage to get him up and safely out of the building. Meanwhile Casey and Severide are still stuck downstairs, the flames closing in on them. Casey manages to get to the higher floor but just as he gets Severide in his grip, the two begin to slip. Just as it looks like Casey can't bear to hold both his own weight and Severide's, Mouch comes out of nowhere and grabs ahold of Casey's feet, helping the two up to safety.
Outside, Gabriela and Leslie are working on Herman, who's badly hurt. He gets sent to the hospital with a possible tension pneumothorax, but the rest of the crew has made it out safely. The following morning, Gabriela receives a call from her lawyer: there's going to be a trial regarding the emergency surgery Gabriela performed on a young patient, even though the patient is stable and is being released from the hospital soon. The crew gathers in the waiting room of the hospital, nervously awaiting word on Herman's condition. Casey steps outside, his face weathered and exhausted with the day's work. He gives Hallie a call and asks her to come over: even with all of their issues, she is still his number-one comfort.