Mr. Ratcliffe had traveled extensively, was a linguist, and a far richer man than his neighbors had supposed. Collecting precious stones had been his hobby, and in a case deposited with his bankers there were many valuable, and some unique, gems. Probably he had others with him in the house, but none were found except the sapphire lying on the blotting-pad. Robbers might have taken them, the marks on the window-sill were suggestive, but I was doubtful on this point. Even if robbers had entered the room, how was Mr. Ratcliffe's death to be accounted for? There was no mark upon the body, there was no trace of poison. The doctors declared he was in a perfectly healthy condition. There was no apparent reason for his death. Besides, if he had been robbed of his jewels, why should the sapphire have been left? It was only natural, perhaps, that suspicion should fall upon the dead man's nephew. Might he not have left the house by the window? it was asked. I had put the same question to myself. Captain Ratcliffe's behavior, however, was not that of a guilty man, although there were certain things which told against him. He answered questions frankly and without hesitation. He was in a line regiment, and was somewhat heavily in debt. It was close upon midnight when he left his uncle, he said, and they had not gone into the study at all. They had sat smoking and talking in the dining room, and just before he left they had both had a little whisky. The empty glasses and the cigar ends in the dining room went to confirm this statement. He knew about his uncle's hobby for stones, was surprised to find that he was such a rich man, and declared that he had no idea he was his heir. Mr. Ratcliffe had never helped him in any way; in fact, that very night he had refused, not unkindly but quite frankly, to lend him a sum of money he had asked for. There had been no quarrel, and they had parted excellent friends. I am convinced that a large section of the public wondered why Captain Ratcliffe was not arrested, and possibly some detectives would have considered there was sufficient evidence against him to take this course. I did not, although I had him watched. The fact was that Christopher Quarles lurked at the back of my mind. I found that he had spoken the truth when he said that he was known at Scotland Yard. He was a professor of philosophy, and some two years ago had made what seemed a perfectly preposterous suggestion in a case which had puzzled the police, with the result that he had been instrumental in saving an innocent man from the gallows. A chance success was the comment of the authorities; my own idea was that he must have had knowledge which he ought not to possess. Now it might prove useful to cultivate the acquaintance of this mysterious professor, so I called upon him one morning in his house at West Street, Chelsea, as keen upon a difficult trail as I had ever been in my life.