The death of Lessingham and his companion, Purvis, was, indeed, a tragic affair; but an automobile accident, especially one occurring in a race, rarely arouses suspicion. Sergeant Showerby, however, was a conscientious soul. His duty was to investigate thoroughly and investigate he did, with results that were suspicious enough to arouse Inspector Hanslet of Scotland Yard and, through him, the great criminologist, Dr. Priestley. At first, there is so little evidence that one cannot understand Dr. Priestley’s interest in the case. Then, one by one, clues appear—not the ordinary clues which fall fortuitously in a detective’s lap, but clues that are found because the Doctor, by his famous process of logical deduction, knows where to look for them. Gradually a pattern forms so diabolical in its simplicity and effectiveness that Dr. Priestley is forced to set a dramatic trap which very nearly ends the lives of both detective and criminal.