Malcolm Sage nodded. "The marks of the cord were clearly defined and reflected in the mirror. Had the key not been touched, it would have helped." "How?" asked Inspector Wensdale. "By means of the string the key is turned only just to the point where the lever falls through the hole to the floor. The fingers would turn beyond that point, not being so delicate." "Mr. Sage, you're a wonder," burst out the inspector. "I then," proceeded Malcolm Sage, "examined all the other doors in the house, and I found that of one room, which I after discovered to be Peters', was heavily scored at the bottom. He had evidently practised fairly extensively before putting the plan into operation. He had also done the same thing with the library door, as there were marks of more than one operation. Furthermore, he was wiser than to take the risk of so clumsy a tool as a lead-pencil. He used this." Malcolm Sage drew from his pocket the roll of twine with the thin steel instrument down the centre. It was a canvas-needle, to the eye of which the cord was attached. "This was absolutely safe," he remarked. "Another thing I discovered was that one lock, and only one lock in the house, had recently been oiled--that of the library-door." Sir James nodded his head several times. There was something of self-reproach in the motion. "Now," continued Malcolm Sage, "we come back to why a man should be sitting at a table absorbed in gazing at nothing, and at a time when most of the household are either in bed or preparing for bed." "Peters said that he was checking his pass-book," suggested Sir James. "That is undoubtedly what he _was_ doing," continued Malcolm Sage, "and Peters removed the passbook, put it in a drawer, first destroying the cancelled cheques. He made a blunder in not replacing the pass-book with something else. That was the last link in the chain," he added. "I don't quite see----" began Sir James. "Perhaps you did not read of a case that was reported from New York some eighteen months ago. It was very similar to that of Mr. Challoner. A man was found shot through the head, the door being locked on the inside, and a verdict of suicide was returned; but there was absolutely no reason why he should have taken his life. "What actually happened was that Mr. Challoner went to his bank to draw five hundred pounds with which he hoped to bribe his nephew's fiancée. He trusted to the temptation of the actual money rather than a cheque. When he was at the bank the manager once more asked him to return his pass-book, which had not been balanced for several months. He was very dilatory in such matters." "That is true," said Dane, speaking for the first time.