"Mr. Wildred was away when we first arrived at the House by the Lock, sir," he went on, "but we should have made use of our search-warrant without waiting for his return had not the passage and the octagonal room you described, as well as the tower, been shut off from all communication with the older part of the house by a heavy iron door, of which Mr. Wildred invariably carries the key. This his butler explained by saying that the door had been placed on account of his master's chemical experiments, which were sometimes of a slightly dangerous character, unless great precautions were used, and in case of an explosion or other accident the safety of the living-rooms might be assured by means of the iron door. The only way of opening it would have been to employ dynamite, the lock being impregnable; and as the grounds for suspicion against Mr. Wildred were not yet strong enough to resort to such violent means, there was nothing to do but wait. He was wired for to London at once." "Naturally he would prefer being on the spot," I said, with something like a sneer. "All the same, I am very sure that there _is_ another means of communicating with the octagonal room and the tower besides the main door through the passage." And I mentioned the mysterious disappearance of the servant, which had on Christmas Day led me to believe in the existence of a secret way of exit. "We did look about for something of the sort, and even went down a cellar," said the detective, "but saw not the slightest sign to suggest a hidden door." "Well, go on then to Mr. Wildred's return," I exclaimed impatiently. "I am anxious to learn why it has been decided that I put you on the wrong track." "When he came home he admitted very frankly that he had been annoyed at the bother occasioned by our telegram, but appeared by that time to have recovered from his vexation, and to be inclined to laugh the matter off. He let us know in a moment that he guessed how the information had come, but we said nothing, of course, to confirm his suppositions. "In the first place he opened the iron door, explained its workings as though he took some pride in its mechanism, which he said he had invented himself. Then he showed us into the octagonal room, which he had had fitted up as a studio and smoking-room combined. The little door you had seen behind the drapery merely led into a cupboard containing boots, an artist's model--a jointed figure of wood--and other odds and ends. It was concealed only because it was not 'an object of beauty,' Mr. Wildred said.