I took his arm, and holding the rail with the other hand staggered up into the box and sat down on the bench. "Yes, it has been a near shave," I said; "and a big price to pay for solving a mystery." "Do you mean to say you know what it is?" asked Henderson eagerly. "Yes," I answered, "I think I know now; but first tell me how long was I unconscious?" "A good bit over half an hour, sir, I should think. As soon as I heard you call out I ran down as you told me, but before I got to you I nearly fainted. I never had such a horrible sensation in my life. I felt as weak as a baby, but I just managed to seize you by the arms and drag you along the line to the steps, and that was about all I could do." "Well, I owe you my life," I said; "just hand me that brandy flask, I shall be the better for some of its contents." I took a long pull. Just as I was laying the flask down Henderson started from my side. "There," he cried, "the 6.30 is coming." The electric bell at the instrument suddenly began to ring. "Ought I to let her go through, sir?" he inquired. "Certainly," I answered. "That is exactly what we want. Oh, she will be all right." "No danger to her, sir?" "None, none; let her go through." He pulled the lever and the next moment the train tore through the cutting. "Now I think it will be safe to go down again," I said. "I believe I shall be able to get to the bottom of this business." Henderson stared at me aghast. "Do you mean that you are going down again to the tunnel?" he gasped. "Yes," I said; "give me those matches. You had better come too. I don't think there will be much danger now; and there is daylight, so we can see what we are about." The man was very loth to obey me, but at last I managed to persuade him. We went down the line, walking slowly, and at this moment we both felt our courage revived by a broad and cheerful ray of sunshine. "We must advance cautiously," I said, "and be ready to run back at a moment's notice." "God knows, sir, I think we are running a great risk," panted poor Henderson; "and if that devil or whatever else it is should happen to be about--why, daylight or no daylight----" "Nonsense! man," I interrupted; "if we are careful, no harm will happen to us now. Ah! and here we are!" We had reached the spot where I had fallen. "Just give me a match, Henderson." He did so, and I immediately lit the lamp. Opening the glass of the lamp, I held it close to the ground and passed it to and fro. Suddenly the flame went out. "Don't you understand now?" I said, looking up at the Inspector. "No, I don't, sir," he replied with a bewildered expression. Suddenly, before I could make an explanation, we both heard shouts from the top of the cutting, and looking up I saw Bainbridge hurrying down the path. He had come in the dog-cart to fetch us. "Here's the mystery," I cried as he rushed up to us, "and a deadlier scheme of Dame Nature's to frighten and murder poor humanity I have never seen."