Hercule Poirot is summoned to France after receiving a distressing letter. Upon his arrival in Merlinville-sur-Mer, the Belgian investigator finds the man who penned the letter, millionaire Renauld, stabbed to death near a golf course. Poirot initially discovers that Renauld and his wife were victims of an apparent break-in, resulting in Renauld's kidnapping and death. While in the midst of investigating Renauld's death, the killer strikes again, forcing Poirot to consider alternative suspects.