The premise of the book is that everyone who has ever died has gone to Styx, the river that circles the underworld. The book begins with Charon, ferryman of the Styx being startled and annoyed by the arrival of a houseboat on the Styx. At first afraid that the boat will put him out of business, he later finds out that he is actually to be appointed the boat's janitor. What follows are eleven more stories (for a total of twelve) which are set on the house boat.
After the House-Boat was hijacked by Captain Kidd at the end of A House-Boat on the Styx, the various members of its club decided that in order to track it down, a detective would have to be called in. So they hired Sherlock Holmes, who, at the time of the book's publication, had indeed been declared dead by his creator.