I stood quite still, gripping the boat-hook in my hand, and looking right and left, straining my eyes for the slightest movement of anything around, when suddenly, close below me from the water, inside the lock, came a loud cry-- "Open the lock, for God's sake, open the lock!" I started back, feeling my hair rise and stiffen. The sound echoed and reverberated through the silent night, and then died away; but before it had done so I had sprung to the great beam and closed the upper gate. As I did so I caught sight of the old man trembling and shaking at the door of the cottage. I called to him to go and watch the upper gate, and, racing down to the lower ones, wound up one of the sluices with a few pulls, so as to let out the water with as little escape room as possible. I knew by this means if there were any creature of tangible form in the water we must find it when the lock was emptied, as its escape was cut off. [Illustration: "Struck it a terrific blow with the boat-hook." A Master of Mysteries.--Page 167] Each of the following minutes seemed stretched into a lifetime as, with eyes riveted on the dark water in the lock, I watched its gradual descent. I hardly dared to think of what I expected to see rise to the surface any moment. Would the lock never empty? Down, down sank the level, and still I saw nothing. A long, misshapen arm of black cloud was slowly stretching itself across the moon. Hark! there was something moving about down in the well of darkness below me, and as I stood and watched I saw that the water was uncovering a long, black mass and that something ran slowly out of the water and began to clamber up the slimy, slippery beams. What in the name of heaven could it be? By the uncertain light I could only see its dim outline; it seemed to have an enormous bulbous head and dripping, glistening body. The sound of a rapid patter up the tow-path told me that the old man had seen it and was running for his life. I rushed down to where the thing was, and as its great head appeared above the edge, with all my force struck it a terrific blow with the boat-hook. The weapon flew into splinters in my hand, and the next moment the creature had leapt up beside me and dashed me to the ground with almost superhuman force. I was up and on to it again in a second, and as I caught and closed with it saw that I had at least to deal with a human being, and that what he lacked in stature he more than made up for in strength. The struggle that ensued was desperate and furious. The covering to his head that had splintered the boat-hook was, I saw, a sort of helmet, completely protecting the head from any blow, and the body was cased in a slippery, closely fitting garment that kept eluding my grasp. To and fro we swayed and wrestled, and for a moment I thought I had met my match till, suddenly freeing my right arm, I got in a smashing blow in the region of the heart. The creature uttered a cry of pain and fell headlong to the ground.