Inspector Hanslet was rapidly becoming the foremost figure at Scotland Yard. He was a man who, without being brilliant, possessed more than the usual quickness of perception. He could, in his own phrase, see as far through a brick wall as most people, and to this attribute he added an agility of mind remarkable in a man whose training had been of a stereotyped kind. Early in his career he had become acquainted with Dr. Priestley, and the Professor, to whom a problem of any kind was as the breath of his body, had since encouraged him to come to Westbourne Terrace and discuss his difficulties. To many of these the Professor’s logical mind had suggested the solution. Since he refused to allow his name to be mentioned, the credit for his deductions descended upon Hanslet. As a matter of fact, the authorities knew very well how matters stood, and Hanslet was always employed upon those cases which promised to be complicated, since it was an open secret that he could call upon the advice and assistance of Dr. Priestley.