12-year-old Jonathan has been expelled from innumerable schools. His stepfather has now decided that he is to have one last chance at the St. Thomas boarding school in Leipzig with its world famous boys choir. At the airport, Jonathan adopts an abandoned dog, but animals are prohibited at school. The other boys help him to hide the dog in a disused railway wagon. One day, however, a stranger appears, he promises to help the boys, takes over the dog and appears to be very well informed about life at the St. Thomas boarding school.