The door with seven locks

As a practical joke, Sub-Inspector Dick Martin, about to retire, is asked to find a stolen library book. Before long, Dick finds himself intrigued by the nature of the book—and the attractiveness of Sybil, the librarian. Now in private practice, Dick accepts a job that requires him to chase an elusive nobleman, Lord Selford, across the world and is subsequently surprised to find that his favorite librarian is Selford’s relative. Events take a turn when a safe-cracking expert is murdered after attempting to break into the Selford family crypt, and Dick investigates. The Door with Seven Locks contains the locked-room puzzle for which Edgar Wallace was famous, but it’s also notable for its exploration of the concept of nature versus nurture.