On a lecture/vacation visit to Paris, Dr. Ordway drops in on his friend, the Prefecture of Police. He becomes involved in a case involving the stabbing of an old man. The man's son, not all that mentally stable, believes he killed his own father in a rage because his father disliked his new bride, the daughter of a cabaret knife-thrower. Investigating the case, Ordway finds that the business of the legal copying art masterworks may also be involved.