“It’s a big corner stone,” she said, in a low voice. “It swings round and opens like a door. It’s the way the old Abbot used to go out when he carried on with Lady Chelford--you’ve heard that bit of scandal, I suppose?” The “bit of scandal” was some eight hundred years old and was news to him. “If you’ve got a lamp you can put it on.” He pulled out his torch and turned the switch. They were in a tiny stone chamber at the top of a circular flight of moss-grown stairs. Above was a vaulted roof, which seemed to be cut out of one piece of stone, as it might well be, for the interior measurements of the tower could not have been much more than four by five. The thickness of the walls he could judge; they had been built in the days when walls had other functions than to support a roof. “Come along.” She led the way, stepping gingerly on the slithery moss. He counted twenty-five steps, and then they were in a large stone chamber, so weatherworn that it seemed to be a natural cave. Walls and roof had lost their symmetry, and only the square of it told him that it was the work of man’s hands. “Have you got the key?” He nodded. Many years before, Gwyn & Gwyn had defended a famous burglar and had secured his acquittal on a technical error in the indictment. In reward he had presented to his lawyer a key which he claimed would open any door, big or small. It was a curious contrivance, consisting of a steel rod into the end of which strangely shaped projections could be screwed. Arthur had given it to his head clerk as a souvenir, having no interest in such matters himself, and rather scandalized that the firm was engaged in so discreditable a business as defending a burglar. This souvenir had now become an instrument of providence. “Here is the place.” She still spoke in a whisper, though it was hardly likely they could be overheard. In each corner of the room, facing them as they turned from the foot of the stairs, was a small, narrow door, deeply recessed. They reminded Mr. Gilder of the cell doors in Dartmoor, and there was a further likeness in another respect. Near the top of the left-hand door was a tiny iron grille, consisting of three rusted bars. “Look!” she whispered. He flashed the light of the lamp inside, where a deep, narrow cavern showed, along two sides of which ran a stone bench, and on the bench were innumerable cylinders of significant shape. He inspected the nearest; there was a curious seal at one end. Fabrian Gilder’s heart beat faster. The girl’s hand that held his arm tightly was trembling. “I’m so frightened,” she whimpered. “What are you frightened about?” “I’m so afraid of that awful Black Abbot.” She was on the verge of hysterical breakdown. He must work quickly.