Lucy Bailey is not a girl to take no for an answer. When she asks her friend Billy to help her rescue a stray dog, she has no idea of the potential repercussions. A serious crime is committed while Billy is absent from the children's home where he lives and, when suspicion falls on him, the police decide to lock him away in a mental institution. Lucy refuses to believe Billy has done anything wrong, and enlists her teenage brother Arnold to help. It looks as though Billy's freedom will soon be won - before Arnold too falls foul of the law...