To Captain Ducie it seemed plain enough why these rooms were kept untenanted, and the door at the extreme end of the corridor nailed up. M. Platzoff evidently did not choose that any one should come into too close proximity to the room within which lay the secret of the hidden door. For that the hidden door was in the library everything he had discovered that night went indisputably to prove. He relocked the four rooms, and went back to the library musing upon all he had seen. He was just about to shut and fasten the curtained door when a sudden thought struck him and caused him to pause. He stood musing for a few moments, his face gradually brightening the while, and then taking up his candle, he retraced his way to the fourth room in the corridor. He went in, put down his light, and succeeded after some difficulty in unfastening the shutters, which were strongly barred with iron. This done, he shut up his candle for a while in an empty wardrobe, and then proceeded to fold back the shutters. The night was a fine one, and the stars afforded him sufficient light for what he wanted to do next. Between the shutters and the window was a faded green blind, at present drawn up about three parts of the way to the top. From this blind depended a green cord that ended in a tassel. In this cord Captain Ducie tied a simple slip knot. When this was done, he unhasped the window, and tried whether the lower sash would work up and down readily and without too much noise. Finding that the window worked satisfactorily, he left it unfastened, and then proceeded to put back the shutters, which also he left unbolted. Then he took his candle out of its hiding-place and went back to the library, closing behind him both the door that led into the corridor and the curtained door, but leaving them both unlocked. Midnight was now close at hand, and it was necessary that he should get back to the smoke-room. But even with more time at his command, he could have done nothing more to-night. When he got back to the smoke-room, he found Platzoff to all appearance precisely as he had left him. He put back the pass-key into the pocket from which he had taken it, and unbolted the outer door. Ten minutes later Jasmin, the new valet, acting temporarily in place of Cleon, coming into the room, found Captain Ducie quietly smoking beside the comatose body of his master. CHAPTER XIV. AT THE CURTAINED DOOR.