Lucy Bailey is not a girl to take no for an answer. When she asks her friend Billy Wellington 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 that the safest thing for everybody is to lock him away in a mental institution.

Lucy refuses to believe that Billy has done anything wrong, and enlists her cool-headed teenage brother Arnold to help. DI Daniel Earnshawe, who has his own doubts about the police's conclusions, turns out to be unexpectedly helpful, and Billy has someone else on his side too: Helen Durkin, a beautiful, damaged girl who has been seeking to make amends for her past.

With so many daring and resourceful people battling on his behalf, it looks as though Billy's freedom will soon be won - before an unexpected development sees Arnold too fall foul of the law. Refusing to give up hope of winning freedom for them, Lucy chases up the few remaining clues while Daniel and Helen resort to an alternative form of justice . . .