The more Tanner thought over it, the more likely this theory seemed. It would explain the facts generally, as well as the secrecy with which both parties had acted. And yet there were difficulties. This annuity business was a difficulty. From Douglas’s point of view it was easy enough to understand. If the blackmailer thought his receipts were precarious, or if time was reducing or about to reduce the value of the secret, it would be a natural step for him to try to convert his vanishing doles into a fixed and certain income. But Sir William’s motive would be different. His only hold on the preservation of his secret was the expectation on Douglas’s part of sums yet to be paid. If the manufacturer agreed to the annuity his hold would be gone. That he should do so was inconceivable to Tanner. And yet apparently he had. He had at least written the £3000 cheque. But the second difficulty to the blackmail theory was more serious. The wrong man had been murdered! If Douglas had been the victim it would have fitted in well enough. It would have been argued that Sir William had taken a desperate remedy to escape from an intolerable situation. But Sir William’s death would have been the last thing Douglas could have desired. He would never have cut off the source of his income. No; attractive as the blackmail theory had seemed at first, Tanner found its difficulties rather overwhelming. He had by this time reached the Yard, and sitting down at his desk, he lit a cigar, and continued his ruminations. Suppose again that blackmail had been levied, where did Austin and Cosgrove come in? They must in this case obviously have taken sides. Either they must have been assisting Sir William to extricate himself, or else they must have been party to the blackmail. But as Tanner pondered these alternatives, he could not see how either would meet the facts. If the cousins were acting for their relative, they obviously would not have murdered him—it was a contradiction in terms. Here again the wrong man had been killed. On the other hand, it was difficult to see how they could have been in league with Douglas against Sir William. Anything discreditable to the manufacturer would react on both the son and nephew, and their threat to make the matter public would therefore hardly be convincing. For their own sakes the cousins would be as anxious as Sir William to keep the thing quiet. It was also clear to Tanner that they would never have put themselves in the power of a man like Douglas. If they had wished to murder Sir William for his money, they would have done so at some time when Douglas would not have witnessed the crime. So far had Tanner progressed when he realised his argument really was that Sir William could not have been murdered at all! He swore angrily, and went back to see the point from which he had started. Blackmail. It would seem, then, that blackmail could not be the explanation. And yet . . . It was an attractive theory . . .