This text presents a series of logic puzzles, ranging from the simplest problems to the most tantalizing complexities. An array of imaginary characters - sane and insane vampires, psychiatrists, dreamers, hermits, kings, knights and knaves - pose questions, giving just enough information to enable the reader to solve problems of increasing difficulty. The final section of the book, "The Mystery of the Monte Carlo Lock", is a mathematical novel. Beginning with the problem of finding a combination to open a safe, Inspector Craig of Scotland Yard finds himself in ever deeper mathematical waters, which lead eventually to the very heart of Godel's revolutionary theory of undecidability.