A mixture of a psychological study of a ten-year-old boy, an English domestic comedy and a satire on psychologists finds young Johnny Brent, the only child of a pair of psychologists, trading an "invisible watch" to a much-younger child for a large magnet. His nurse/nanny accuses him of stealing and scolds him and he runs away. He soon convinces himself that the police are after him and following several unsuccessful attempts to get rid of the magnet, he presents it to an organizer of a fund-raising campaign for acquiring an iron-lung for the local hospital. The magnet is one of the auction items and finally is mounted on the iron-lung as a tribute to the unknown donor. Meanwhile, the father makes a completely inaccurate diagnosis for the mother of the boy's worries. In the end the boy meets the child he thought had died as a result of losing the magnet, and trades the boy...