The two proceeded in the dark to the head of the staircase. With their heels they verified the last step; then Juve said in a low voice: "I will go forward four paces. I am now in the middle of the landing; I lift the curtain, turn and go in." The steady tick of the little Empire clock on the mantelpiece assured Juve that he was indeed in the study. "Well, here I am," and mechanically he flung his hat on the sofa. But scarcely had he uttered these words when Fandor's voice, very clear, but some way off answered "I am in the study, too." Juve now switched on the light. Fandor was not there. Rushing back to the landing he ran full tilt into his friend and the two gripped each other in amazement. "Look here," exclaimed Fandor, "if I'm not mistaken, you turned to the right past the curtain while I went to the left; there may be two separate entrances to the study." "Let us keep together this time," replied Juve; "I propose to get to the bottom of this mystery." As they came out of the darkness of the passage and plunged into the full light of the room, Juve stopped short. His hat was no longer on the sofa. Fandor went to the mantelpiece, turned and confronted the detective. "I stopped the clock some moments ago, and here it is going and keeping exact time! How do you account for it?" Juve was about to reply, when suddenly with a dry click the light went out. Fandor, at the same moment, gave a startled cry: "Juve! the door is fastened; we are shut in!" With one bound Juve leaped for the window; but after opening the casement he perceived that thick iron shutters, padlocked, banished all hope of escape in that quarter. Fandor was ashy pale; Juve staggered as he moved toward him. "Walled in!" he cried. "We are walled in!" But a new terror suddenly confronted the two men. The floor appeared to be giving way, and as the descent proceeded regularly, they realised that they were in a strange form of elevator. The study, however, did not drop very far. With a slight shock it reached the end of the run and stopped short. Juve cried with an air of relief, "Well, here we are, and it now remains to find out where we are." The existence of two studies identical in every particular, one of which was housed in an elevator, explained not only the events of the evening, but also the tragedy of two days before. "Juve! did you feel anything?" "Yes." "What is it?" "I don't know." Both had just experienced a weird sensation, impossible to define. Upon their hands and faces slight prickings irritated the skin. The air at the same time seemed heavier and more difficult to breathe. There was, besides, a soft, vague crackling. With some difficulty Juve lighted his pocket-lamp. By its faint glimmer the two men made a discovery. A fine rain of sand was falling from the ceiling. "It's collapsed!" cried Fandor. "We're done for!" replied Juve. They passed through some awful moments. All around the sand gathered and rose.