The tale represents the only occasion on which Stevenson was drawn to adopt the mystery type of novel in which the reader is carried forward by the incidents surrounding a secret which is kept to the last. As explained in the Epilogue, familiarly addressed to his friend, Will H. Low, he had aimed at giving greater realism to this form of story by a more gradual approach to the essence of the yarn. The reader is allowed first to live with the characters for a while instead of stepping with them into their adventures straight on his introduction to them. Hence the first half-dozen chapters, with their scenes in Paris and Edinburgh, are almost without bearing on the incidents afterwards developed, and might well be cited against Stevenson's doctrine that the opening of a story is of a piece with its end. Evidently the Prologue, anticipating Dodd's adventures, is used as a device to cast unity over the whole in something of the manner of Mr. Conrad.