Tom's Enemy

When a sixteen year old boy is taken prisoner by a young German submariner on a popular holiday beach in Norfolk, he has no idea how to escape from the deadly situation...especially as WW2 has been over for more than fifty years.  That is the immediate problem.  Somehow he has managed to travel back in time and he has no idea how to return to his own time.  He can't ask anybody to help him because nobody would believe him.  All he can do is try to escape his captor by helping him to get home.