It was exactly three months after the startling termination of the Scarab murder case[1] that Philo Vance was drawn into the subtlest and the most perplexing of all the criminal problems that came his way during the four years of John F.-X. Markham's incumbency as District Attorney of New York County. Indeed, so mystifying was this case, so apparently inexplicable were its conflicting elements, that the police were for adding it to their list of unsolved murder mysteries. And they would have been justified in their decision; for rarely in the annals of modern crime has there been a case that seemed to reverse so completely the rational laws by which humanity lives and reasons. In the words of the doughty and practical Sergeant Ernest Heath of the Homicide Bureau, the case "didn't make sense." On the surface it smacked of strange and terrifying magic, of witch-doctors and miracle-workers; and every line of investigation ran into a blank wall. In fact, the case had every outward appearance of being what arm-chair criminologists delight in calling the perfect crime. And, to make the plotting of the murderer even more mystifying, a diabolical concatenation of circumstances was superimposed upon the events by some whimsical and perverse god, which tended to strengthen every weak link in the culprit's chain of ratiocination, and to turn the entire bloody affair into a maze of incomprehensibility. Curiously enough, however, it was the very excess of ardor on the part of the murderer when attempting to divert suspicion, that created a minute hole in the wall of mystery, through which Vance was able to see a glimmer of light. In the process of following that light to the truth, Vance did what I believe was the shrewdest and profoundest detective work of his career. It was his peculiar knowledge of special and out-of-the-way facts, combined with his almost uncanny perception of human nature, that made it possible for him to seize upon apparently unimportant clues and resolve them into a devastating syllogism.