This novel is an excellent example of the inverted detective story, a modern form that R. Austin Freeman is credited with inventing. You know from the beginning who the guilty party is, but watching Dr. Thorndyke figure it out is amazing. And watching the perpetrator think that he is getting away with his crime, while watching Dr. Thorndyke close in on him is well-done literary irony. The fun comes not from being baffled, but from watching Thorndyke's mind at work and observing his scientific methods - which include, in this case, geology, petrology, psychology, marine biology, handwriting analysis, and chemical analysis. The crime takes place in a yacht off the coast of Penzance in Cornwall, where a circle of friends are vacationing. The victim is a boorish, overbearing, dishonest brute with money. The murderer is a likable, gentlemanly, talented artist of modest means. Every one likes the murderer, including Dr. Thorndyke.