Harri sees the dead boy’s blood outside Chicken Joe’s, and Jordan bets him to touch it. A pigeon walks past indifferently. Harri was “half friends” with the dead boy, who was older and went to a different school. Harri lives on the ninth floor of Copenhagen House, one of three fourteen-story tower blocks.
Harri talks to Papa on the phone and tells him that a pigeon flew into their house. His older sister Lydia was terrified, but Harri caught the pigeon and released it from the balcony. Harri’s baby sister, Agnes, lives with Papa and Grandma Ama back in Ghana, while Harri and Lydia live with their Mamma in London. Harri explains that soon the family will be reunited again. He tells the reader that, back in Ghana, he once saw the body of a boy who had been killed.
At school one day, a boy called X-Fire demonstrates what it’s like to shank someone, using Harri as an example. There is a blonde girl in Harri’s class called Poppy Morgan who makes his “belly turn over” when she smiles at him. Later, when Harri comes home from school, there are cops outside of his tower block. The cops question him and his friends about the dead boy. That night, while standing on his balcony, Harri sees a man below pulling a knife out from under the bin. Harri thinks that this man might be the murderer, but the helicopter circling overhead doesn’t see the potential suspect.
Lydia’s friend Miquita comes over and claims that it was the dead boy’s own fault for getting killed because he shouldn’t have been “fronting.” Harri tells her that she doesn’t know what she’s talking about. Later, Harri asks his friend Dean if he thinks Miquita is right.
Harri attends the dead boy’s funeral. After, he and Dean watch the crowd, checking for suspicious activity. Harri explains that X-Fire is the leader of the Dell Farm Crew. X-Fire pressures Harri into joining the crew, telling Harri that if he sets off the fire alarm at school he can join. Harri tries to set off the alarm but doesn’t manage to break the glass. He runs and hides, fearing that the Dell Farm Crew are now his enemies.
Harri and Dean now consider themselves “proper detectives” on a mission to find out who killed the dead boy. Harri also befriends a Somali boy named Altaf, even though he’s “not supposed to talk to Somalis because they’re pirates.” Harri and Dean interview “suspects” at the pub. Later, Harri sees Lydia pour bleach all over something inside the washing machine at the laundromat. Harri realizes that inside the machine are boy’s clothes that are red like blood. Dean and Harri use sellotape to check for fingerprints around the scene of the crime.
Auntie Sonia later tells Harri that she burns off her fingerprints to avoid getting caught by the police and deported. She is a cleaner who has traveled all over the world, including to America. At school during afternoon registration, Poppy gives Harri a note asking if he likes her. He plans to give the note back to her after the Easter holiday, hoping his answer is the right one.
In May, there is a carnival in Harri’s neighborhood. On Sunday, church is cancelled because someone smashed the windows and wrote DFC all over the wall. Harri argues with Lydia about the clothes she bleached. Harri insists he saw blood on them, but Lydia tells him that it was Miquita’s blood—“girl’s blood.”
X-Fire, Dizzy, Killa plan to rob someone and force Harri to help. Harri is horrified to realize that the chosen target is Mr. Frimpong, the eldest member of his church congregation. While the other boys push Mr. Frimpong over and stamp on his groceries, X-Fire searches the old man’s pockets for his wallet and threatens to stab him if he doesn’t give it up. Horrified, Harri runs away. X-Fire later warns Harri not to tell anyone about what happened. In church on Sunday, Mr. Frimpong reveals his infected knee and laments that in England no one ever helps strangers on the street.
Dean and Harri try to train Terry Takeaway’s dog, Asbo, to recognize evil in order to help them find the killer. Asbo attacks Killa, which makes Harri think their training has worked. Jordan encourages Harri to get a knife, claiming that “everyone needs one.” Poppy is now Harri’s girlfriend. Harri collects the fingerprints of innocent people so he can compare them to those of the suspects. He then attempts to freeze off his own fingertips by holding them in the freezer.
One day, while Miquita is straightening Lydia’s hair, she burns Lydia’s cheek on purpose, asking, “Are you with us or against us?” Lydia assures her she is with them. After school, X-Fire and Dizzy chase Harri and threaten to kill him, but they eventually walk away.
Chanelle and Miquita get into a fight at school one day. Right as Miquita is about to push Chanelle through the window, teachers come over and break up the fight. Harri notices that Killa displays several “signs of guilt,” and Harri begins to believe that Killa murdered the dead boy with Miquita. Harri and Dean grab Killa’s hands and take his fingerprints with sellotape.
Agnes has a fever, and Harri worries that she is going to die. When her fever goes away, Mamma and Lydia both cry with happiness. Auntie Sonia and her abusive boyfriend Julius buy presents for Lydia and Harri. As a birthday surprise for his sister, Harri takes Lydia to some wet cement, where they both leave footprints and write their names. While Dean and Harri are playing football, Dean finds a wallet, inside of which is a photo of the dead boy smiling with a white girl. The boys discover that the photo has blood on it.
While at Lydia’s house, Miquita tells Harri that she’s going to teach him how to kiss. However, when Miquita forces Harri’s hand inside her vagina, Harri pushes her away. Miquita and Lydia get into an argument, during which Lydia implies that Killa is a murderer.
Someone has scratched the word DEAD onto Harri’s family’s front door. Later, the Dell Farm Crew approach Harri and Dean and try to rob them. Harri is carrying the wallet with the dead boy’s picture inside, and when the Dell Farm Crew grabs the wallet, the picture drops to the floor. Killa is visibly upset, and X-Fire burns the picture with a lighter. Just as X-Fire reaches for his knife and is about to pounce on Dean and Harri, Lydia shouts, and the three of them escape to the library together. Lydia explains that she filmed the whole scene, including X-Fire burning the picture.
Someone sets the local playground on fire, but firemen arrive and put the fire out. On the last day of school, Harri watches with delight as the Year 11 kids celebrate their newfound freedom. He and Poppy hold hands, and she kisses him. Harri runs home, shouting his love for Poppy, the pigeons, and the trees. When Harri is almost home, a boy jumps out and stabs him.
As Harri lies on the ground clutching his stab wound, a pigeon comes toward him and says that Harri will be “going home soon.” The pigeon tells him not to be afraid. Harri tries to picture Agnes’ face but cannot, because “all babies look the same.”