Long Way Down follows fifteen-year-old William Holloman during the two days after his beloved older brother is shot and killed. At the beginning of the novel, which is written in verse, Will assures his reader that his story is true, though he suspects the reader won’t believe him. At the start of things, Will is standing outside, talking to his friend Tony about whether they’ll grow taller and thinking about how his brother Shawn had a growth spurt when he was Will’s age. Suddenly, the two hear gunshots. They fall to the ground, as they’ve done many times before in their neighborhood, hoping to stay alive. When the gunshots stop, Will sees that his brother has been shot. Shawn’s girlfriend and mother come to mourn and cry over his body. Will notices that the moon, which normally brings him comfort in hard times, has gone dark. He notices, too, that his brother’s blood looks like chocolate syrup. Back at home, Will buries his head under his pillow to block out the sound of his mother’s mourning, crying, and drinking. He looks around the room that he shared with his brother before his death, and it feels cut in half. He notices the middle drawer of Shawn’s dresser, which is askew, the only thing out of place in the room. Will reaches inside to get Shawn’s gun.  

Will reviews The Rules, the code of conduct to live by in their violent community, which is plagued by gang warfare and police brutality. The Rules are simple. #1: Do not cry, no matter what. #2: Do not snitch, no matter what. #3: Get revenge. Obeying The Rules, Will doesn’t cry after his brother dies. He doesn’t tell the cops anything he knows, and neither does anyone else in the neighborhood. Despite having never held a gun before, Will plans to kill the person he thinks shot his brother: Carlton Riggs, a former friend of Shawn’s who is a member of the Dark Suns gang. Determined to get revenge, Will wakes up the next morning, tucks the gun in his waistband, and sets out for Riggs’ house where he plans to shoot him when he opens the door. 

The majority of Long Way Down takes place during a single elevator ride between Will’s apartment on the 7th floor to the Lobby. Will thinks about how when he and Shawn were little, they would avoid pressing the L button because L meant loser and would laugh at those who did press it, the losers. A man gets on the elevator and begins eying Will. Will feels like a girl who is being checked out at the bus stop. Will confronts the man, who reveals that he’s Buck, a man who Will knows to be dead. Thinking that he might be about to die, Will is frightened. He remembers how Buck took Shawn under his wing after their father died and became like an older brother to him. Buck asks Will what he’s doing with his gun, and the two wrestle over the gun. Buck eventually gives it back to Will and lights a cigarette, filling the elevator with smoke.  

When the elevator stops on the 6th floor, a beautiful teenage girl gets on. Will is attracted to her and glad that she sees the smoke because it makes him feel less insane. She says that she thought people weren’t supposed to smoke on elevators and weren’t supposed to have guns. She asks why he has the gun, and Will says they don’t know each other well enough to have that conversation. She says that they do know each other. She shows him a picture, and he remembers her, Dani, from when they were eight years old. She kissed him and then was shot and died before his eyes. Dani takes one of Buck’s cigarettes, and the elevator stops on the 5th floor. 

Will’s Uncle Mark, who is also dead, gets on the elevator. He’s impeccably dressed and greets Will, who begins to remember details about his uncle, such as his dream of becoming a filmmaker. To get money for a camera, Uncle Mark sold drugs, which eventually lead to him being shot on his corner. Together, Uncle Mark and Will script Will’s revenge plot as though it’s a movie. When it comes to the point in the movie where Will shoots Riggs, he struggles to say the words. Buck steps in and says "shoot" for him. Uncle Mark begins to smoke a cigarette, and the elevator stops on the 4th floor. 

Mikey Holloman, Will and Shawn’s father, who Will calls Pops, gets on the elevator. Will doesn’t remember much about his father, as he died when Will was three. Will and his father embrace, and Will feels the healing power of his father’s love, making some of the bad sensations go away. Uncle Mark and Pops tell Will what really happened with Uncle Mark’s murder. Following The Rules, Pops got revenge on the person he thought killed his brother, but it turned out that his father killed the wrong person. Will is disappointed and even a little ashamed that his father got it wrong. His father hugs him again, grabs the gun, holds it to Will’s temple, and cocks it. Aware that the gun is very real, Will wets himself in fear. Pops gives the gun back, and Will screams in rage and humiliation.  

Pops starts smoking a cigarette and the elevator stops on the 3rd floor. A man who Will doesn’t know gets on the elevator. Will learns the man is Frick, and he’s the man who killed Buck. They tell the story of Buck’s death, when Frick killed him during a robbery gone wrong. Shawn got revenge by killing Frick with a single bullet, which accounts for the missing bullet in the gun Will carries. When Dani asks if Frick knows anyone named Riggs, he says he doesn’t, suggesting that Will is wrong about his brother’s murderer. Frick lights a cigarette, and the elevator stops on the second floor. 

Shawn gets on the elevator, wearing the clothes he died in. He greets everyone except Will. When Will tries to speak to him, Shawn doesn’t answer. When Will hugs him, Shawn doesn’t hug him back. This reminds Will of when they were younger, and Shawn used to ignore him to punish him for being an annoying kid. Will tells Shawn that he’s following The Rules and is on the way to avenge Shawn’s death. Will feels like he’s about to cry and tries to hold his tears back, but then Shawn starts crying, breaking The Rules. He makes a terrible moaning sound that reminds Will of the gears of the elevator. The elevator finally reaches the lobby. The smoke cloud disperses, and all the dead people get out, leaving Will is alone in the elevator. Finally, Shawn speaks to Will, asking if he is coming.