Billy has been in trouble with the police many times for thieving. He tells people that he has stopped stealing, but in fact he hasn't. He steals a book from a bookshop, takes milk from the milkman and even steals things from the shopkeeper who has given him a part-time job. Billy works part-time delivering newspapers before going to school.
Billy hates school. He is always daydreaming in class, and is often shouted at by his teachers. The headmaster hits him on the palms of his hands with a cane. His worst class is Physical Education. The teacher is very cruel and makes fun of Billy whenever he can. When Billy says he cannot play football because he has no shorts, the teacher makes Billy wear a pair of trousers that are much too big for him. Soon Billy will be old enough to leave school and start a full-time job. But he does not know what he wants to do with his life; all he knows is that he does not want to work down the mine. Billy is not interested in the future. All he is interested in is Kes.
Kes is no ordinary pet. She is a kestrel hawk, a bird of prey that usually lives in the wild. Billy loves Kes more than anything else in the world. He gives her raw beef which he gets from the butcher. He trains to Kes so that she will fly about, before returning to his hand. One day in school Billy tells his class how he trained Kes. They all listen very carefully. The teacher asks Billy if he may watch Kes flying. It is the first time anyone has ever shown any interest in Billy, and the boy is very pleased.
One day Jud leaves some money on the kitchen table with a note telling Billy to bet the money on two horses Jud thinks will win in the horse races. Billy takes the money and spends it on fish and chips for himself. When Jud finds out that Billy has not placed his bets for him, he gets really angry. Both horses won their races, and Jud would have won ten pounds if Billy had bet the money. Jud tries to find Billy at school, but Billy is able to hide. To get his revenge on Billy, Jud decides to let Kes escape from the shed in the garden where Billy keeps her. But when Kes scratches Jud with her claws, he gets mad and kills her.
Billy returns home to find the shed empty. He searches for Kes in the fields calling out her name. Finally he asks Jud what he has done with his pet. He tells Billy he put her dead body in the dustbin.