Christopher Halliday, a sensitive artistic sixteen-year-old boy, bitterly resents the harsh treatment he receives from his unimaginative father, and runs away from home and school in rebellion. He camps in a tree-house in the gounds of Mandeville Park, where he is soon discovered by Margaret Roper, a girl of his own age, and by the mysterious and sympathetic Mr Hughes, who both agree to help him. A friendship is formed between the three of them.