The story begins by introducing us to the Wormsley Common Gang, a group of boys ranging from nine to fifteen years of age, who live in a tough area of London and spend their summer holiday pulling pranks. They gather daily in an empty lot created when bombs dropped on England during World War 2 destroyed the houses that used to stand there. One beautiful old house still stands on the edge of the lot, although it was damaged during the war and is propped up by wooden struts. This house is owned by Mr. Thomas, an elderly, solitary man who used to be a builder and a decorator, and whom the boys derisively call “Old Misery.” The bombing destroyed the house’s plumbing, so Mr. Thomas uses an outdoor lavatory.
The leader of the gang is a boy named Blackie who concerns himself with fairness and with the gang’s reputation. A boy named Trevor, who comes from a more affluent background, but whose parents have fallen on hard times, is the gang’s newest member. Usually the boys would make fun of the name Trevor, but the menacing way he carries himself inspires their respect. They call the new boy “T.” and allow him to enter the group without a humiliating ritual induction. Other members of the group include the young and easily surprised Mike, and the more practical and outspoken Summers.
One day, T. surprises everyone by arriving late to the lot. Blackie interrogates T. about where he has been and it slowly comes out that T. has visited Old Misery and toured around the old man’s home. At first it seems to Blackie that this is unbefitting for a member of the gang, especially because T. describes the home as “beautiful.” But T. reveals that he has planned a prank that will surpass all the gang’s past exploits in daring: he wants to destroy Old Misery’s house while the old man is out of town for the three-day weekend. Blackie raises objections to this plan, but the gang puts T.’s idea to a vote and decides to carry it out.
Blackie is hurt at first to see that T. has replaced him as the leader of the gang, but realizes the exploit would burnish the gang’s reputation around London. He decides to support T. Meanwhile T., who is suddenly imbued with confidence and leadership skill, instructs the boys to bring tools for the destruction, and they promise to meet the next day. When Blackie arrives the next day, he can hear the destruction already going on inside. Walking through the house, he notices how methodically the boys are destroying everything from the floors to the banisters, while leaving the walls intact. T. is sitting and listening to the sounds of destruction. He instructs Blackie to smash up the bathroom and says that he is looking for something special to do.
After the other boys leave at the end of the day, T. shows Blackie the special thing he has found: seventy one-pound notes, Mr. Thomas’s life savings. When Blackie asks if T. means to steal the money, T. responds with anger. He says, instead, that the two of them should burn the money as a celebration. Blackie struggles to understand T.’s motivations, asking whether he hates Old Misery, but T. says that hate and love aren’t real, and all that matters are things. After they have burnt the notes one by one, Blackie and T. race each other home.
The next day the boys continue the destruction. After removing each of the floors of the house, they turn on the water, which pours through the hollow house. At that moment, Mike rushes in with news that Old Misery is returning early from his holiday due to the rain. Summers says they ought to run away before they get caught, but T. is adamant that they finish destroying the house. Summers continues to resist and mocks T. by using his full name, “Trevor.” Before the gang has time to laugh, though, Blackie shoves Summers and throws his support behind T. T. tells Mike to go out and stand near Old Misery’s outdoor lavatory and yell for help. Even though T. is giving the commands, Blackie is the leader once again.
As Old Misery approaches his house, a boy runs up to him and tells him another boy is trapped in the outdoor lavatory. Mr. Thomas is indignant that the boys have broken onto his property, but he hears the yells of the boy supposedly locked in the toilet and allows himself to be hurried along by T., even climbing over his own garden wall.
When Mr. Thomas open the lavatory door to free the boy, he finds himself pushed into the lavatory, with the door is locked behind him. He pleads to be set free, but the boy tells him to keep quiet. He realizes no one is around to hear his cries. From the lavatory he can hear sounds that resemble carpenters at work coming from his house.
The boys finish by hacking away at the walls of the house until the structure balances on just a thin strip of mortar. Next they tie the wooden struts supporting the house to the back of a truck parked in the lot. T. brings Mr. Thomas a blanket and some sandwiches, telling him they don’t want him to be uncomfortable overnight, but also adding, much to Mr. Thomas’s confusion, that Mr. Thomas would no longer be comfortable in his house.
Early the next morning, the lorry driver comes to get his truck. As he pulls out of the lot, he feels something tugging on the back fender. Then there is enormous crash and debris rains down. He hears Mr. Thomas yelling from within the lavatory and frees him. Mr. Thomas cries out when he sees that his house has been torn down, but the lorry driver can’t stop himself from laughing at the spectacle.