What I was. Meg Rosoff

The main character of this book-Hilary-recalls the episode that happened to him at the boarding school for boys. The eastern coast of England, the gloomy swamps, the cold sea, which gradually steps on land... During the run, Hilary meets his peer Finn, who lives completely in loneliness in the old hut on the island, and by all means tries to gain his friendship, but he is so until the end and does not let him in to himself and, it seems, hides some kind of secret...