Rouletabille opened the door of his room and after we had passed in, carefully drew the bolt. I had not had time to glance round the place in which he had been installed, when he uttered a cry of surprise and pointed to a pair of eye-glasses on a side-table. “What are these doing here?” he asked. I should have been puzzled to answer him. “I wonder,” he said, “I wonder if this is what I have been searching for. I wonder if these are the eye-glasses from the presbytery!” He seized them eagerly, his fingers caressing the glass. Then looking at me, with an expression of terror on his face, he murmured, “Oh!—Oh!” He repeated the exclamation again and again, as if his thoughts had suddenly turned his brain. He rose and, putting his hand on my shoulder, laughed like one demented as he said: “Those glasses will drive me silly! Mathematically speaking the thing is possible; but humanly speaking it is impossible—or afterwards—or afterwards—” Two light knocks struck the door. Rouletabille opened it. A figure entered. I recognised the concierge, whom I had seen when she was being taken to the pavilion for examination. I was surprised, thinking she was still under lock and key. This woman said in a very low tone:— “In the grove of the _parquet_.” Rouletabille replied: “Thanks.”—The woman then left. He again turned to me, his look haggard, after having carefully refastened the door, muttering some incomprehensible phrases. “If the thing is mathematically possible, why should it not be humanly!—And if it is humanly possible, the matter is simply awful.” I interrupted him in his soliloquy:— “Have they set the concierges at liberty, then?” I asked. “Yes,” he replied, “I had them liberated. I needed people I could trust. The woman is thoroughly devoted to me, and her husband would lay down his life for me.” “Oho!” I said, “when will he have occasion to do it?” “This evening,—for this evening I expect the murderer.” “You expect the murderer this evening? Then you know him?” “I _shall_ know him; but I should be mad to affirm, categorically, at this moment that I do know him. The mathematical idea I have of the murderer gives results so frightful, so monstrous, that I hope it is still possible that I am mistaken. I hope so, with all my heart!” “Five minutes ago, you did not know the murderer; how can you say that you expect him this evening?” “Because I know that he must come.” Rouletabille very slowly filled his pipe and lit it. That meant an interesting story. At that moment we heard some one walking in the gallery and passing before our door. Rouletabille listened. The sound of the footstep died away in the distance. “Is Frédéric Larsan in his room?” I asked, pointing to the partition.