As he stood there, turning the bit of paper over and over, in his hand, puzzling over the problem, the solution flashed into his mind--a solution so simple, yet, withal, so remarkable, that he hesitated to believe it possible. But a further examination of the paper removed his doubts. Chance had placed in his hands another clue, and the most important he had yet discovered, to help him in the elucidation of the mystery of the murder of Roger Glenthorpe. But to verify that clue it would be necessary for him to descend the pit. CHAPTER XXI An orange crescent of a waning moon was sinking in a black sky as Colwyn let himself quietly out of the door and took his way up to the rise. But the darkness of the night was fading fast before the grey dawn of the coming day, and in the marshes below the birds were beginning to stir and call among the reeds. Colwyn waited for the first light of dawn before attempting the descent of the pit. His plan was to climb down by the creepers as far as they went, and descend the remainder of the distance by the rope, which he would fasten to one of the shrubs growing in the interior. He realised that his chances of success depended on the slope of the pit and the depth to which the shrubs grew, but the attempt was well worth making. Assistance would have made the task much easier, but publicity was the thing Colwyn desired most to avoid at that stage of his investigations. There would be time enough to consider the question of seeking help if he failed in his individual effort. He made his plans carefully before commencing the descent. He first tested a rope he had found in the lumber room of the inn; it was thin but strong and capable of bearing the weight of a heavier man than himself. The rope was not more than fifteen feet in length, but if the hardy climbing plants which lined the sides of the pit were capable of supporting him ten or twelve feet down, that length should be sufficient for his purpose. Having tested the rope and coiled it, he slipped it into the right-hand pocket of his coat with one end hanging out. Next he opened his knife, and placed it with a candle and a box of matches in his other pocket. Then turning on his electric torch, he lowered himself cautiously into the pit by the creepers which fringed the surface. There was no difficulty about the descent for the first eight or ten feet. Then the shrubs that had afforded foothold for his feet suddenly ceased, and the foot that he had thrust down for another perch touched nothing but the slippery side of the pit. Clinging firmly with his left hand to the network of vegetation which grew above his head, Colwyn flashed his electric torch into the blackness of the pit beneath him. One or two long tendrils of the climbing plants which grew higher up dangled like pendulous snakes, but the vegetable growth ceased at that point. Beneath him the naked sides of the pit gleamed sleek and wet in the rays of the torch.