“Why suggest a robbery at Foxhills? For that was what they evidently intended the police to swallow. As a matter of fact, they'd have been much better to have left the thing alone. It was a mistake to fake evidence; it always is. However, they'd done it, and I wanted to know why they'd done it. So, when the Fordingbridges arrived, we went off to Foxhills. “I wasn't surprised to find that the murderers had tried to make the thing convincing by filling that sack with silver odds and ends. I'd almost expected something of the sort. But I don't suppose any of us were misled to the extent the murderers hoped. They thought we'd be delighted to find confirmation of Peter Hay's dishonesty—stuff ready packed up for transport. But what one obviously asked oneself was the question: ‘What's all this meant to cover?’ And the answer was, so far as I could see: ‘The removal of some inconspicuous object whose absence won't be noticed in the excitement over the silver.’ “It wasn't long before I got an inkling of what that inconspicuous object was. Miss Fordingbridge was able to tell us. But, notice, if Miss Fordingbridge hadn't happened to come up to Foxhills when we paid our visit, we'd never have known that the diary was missing. We'd have missed the main clue in the whole affair. That was where we were really lucky, and where Aird & Co. had very hard lines. “There was the diary gone a-missing, anyhow; and the obvious question to ask was: ‘_Cui bono?_ Who stands to score by its removal?’ “You heard the story of the missing nephew and the power of attorney given to Paul Fordingbridge. You could hardly help drawing the obvious conclusion that here at last was a possible motive appearing behind the Peter Hay case. The stake on the table was the assets of the Fordingbridge estate; and that was quite big enough to make murder worth while, if you happened to have a turn for that sort of thing. “But when you come to ask: ‘_Cui bono?_’ you find that the problem's like one of those quadratic equations we used to get at school, where there are two answers and one seems just as good as the other. “Suppose the claimant was an impostor, and see where that leads you. Derek Fordingbridge had spent a lot of time with Peter Hay in earlier days. The chances were that Peter Hay was the only man who could give evidence about their joint doings, and that evidence might form the basis of a damaging examination of the impostor. Further, the diary would be a priceless thing for an impostor to lay his hands on. It would supply him with any amount of irrefutable evidence which he could draw on for his sham recollections. Clearly enough, if the claim was a fraudulent one, then the theft of the diary and the silencing of Peter Hay would fit in very neatly.