"Of course. I knew you doubted me," I answered, smiling. "I'll remain here until you return, though, to be frank, I don't see very much cause for alarm." "I do. There's a mystery here--one which we must fathom. Keep watch. I'll be back in a few moments." And he left the steps and, turning to the left, disappeared round the corner. I stood outside the door, my ears strained to catch the slightest sound. The young man's presence there was indeed an unfortunate contretemps. In the silence I could hear my own heart thumping. Of a sudden, however, I thought I could detect a sound of movement within. I listened attentively. Yes, I was not mistaken, someone was actually in the hall! What if it were the unknown assassin, returned to the scene of his crime? My heart-beats quickened. The dead girl's lover had not been mistaken. The lights had been put out when the person or persons inside were disturbed by his ring. In a few moments he would be there with the police, and the crime would be properly investigated. But what account could I myself give of the reason of my call? If I were suspected, the police might inquire into my movements during the past few days and gain knowledge of my visits there! My position was growing to one of great seriousness. Every moment increased my peril. Across the narrow road rose the great blank wall of a mews, while in the room on the first floor above where showed the high, dark window stretching across nearly the whole frontage of the house, lay huddled, I knew, the body of the dead Professor. I was still listening, full of wonder as to who might be lurking in that house of death, when, of a sudden, I heard the latch touched, and slowly and silently the big door opened. I drew back, prepared for a fight, but next second a cry of amazement escaped my lips when I saw in the darkness of the cautiously-opened door a man's face--the thin, sallow, frightened face of Kershaw Kirk. "It's I, Holford!" he gasped. "I must get away. Langton must not see me. Remember you must not breathe a single word of your knowledge of myself! Success now depends entirely upon your silence. I will wire an appointment with you to-morrow. Be careful, or you yourself may now be suspected." "But why not tell the police?" I demanded, barring his way. "Police be hanged!" he cried impatiently. "Have I not already told you? I have no time to argue. Langton must not see me--he must know nothing of me. A word from you would mean loss incalculable, and all hope of elucidating the mystery would instantly be at an end. Which way did young Langton go?" "Towards Clarence Gate," I replied almost mechanically, for his sudden appearance there had startled me. "Good!" he cried; "then I'll go in the opposite direction. Be silent, Holford, and rely upon me. Whatever you may discover, do not betray any surprise. In this affair you will probably meet with a good deal that will surprise you--as it has already surprised me."