This book is a collection of essays on induction and abduction by several authors mainly know in the field of semiotics, theory of mind, and cognitive science. This makes the essays somewhat heterogeneous, but in a good way. It is a little misleading to say that it is the sign of three, b/c in the book they also look at other people/characters besides (Auguste) Dupin, (Sherlock) Holmes, and (Charles Sanders) Peirce. The sign of three is a play on words from the Sherlock Holmes story 'The sign of four' and the importance of 3 in the philosophy of Charles Sanders Peirce. Other people/characters that they refer to are Freud, Voltaire's Zadig, and Karl Popper.