"Well," he said, "we'll probe this mystery to the bottom. I, too, have heard suspicious noises in the passages to-night, and, coming down, after I had retired, to find out what they were, I was shut out from within, though I don't think they were aware of my presence. We must go round on the outside and see what we can through the windows." "You can't," she said. "The approaches are protected by an iron fence with spikes." "But surely there's a gate?" "Yes, but it's always padlocked." "We'll have a look at it, any way," he replied; and they approached and examined it closely. The Secretary rattled the lock cautiously and found it old and shaky. "I think I could smash this with a couple of bits of flint," he said, "and if I have a new lock put on at my own expense, my hostess will, under the circumstances, probably forgive me." And suiting the action to the word, he managed, by a few judicious blows, with two bits of stone, picked up from the driveway, to bend the hasp of the lock sufficiently to release it. There being no further impediment to their progress they hastened through the gardens, and a moment later were standing outside one of the great hall windows whose lower panes were on a level with their faces. They could distinctly see three people, but their glances were riveted on a circle of light farther up the hall, a circle that shifted and danced over the surface of the secret door, flashing on the heads of the silver nails; a circle that was made by the lens of a small bull's-eye lantern, held in the grasp of a crouching figure whose back was turned towards them. By his side were two others, apparently a man and a woman, who seemed to be directing him at his work. For several minutes the little group presented their backs to the spectators, but at an incautious step of the Secretary's, which caused a dry twig to crackle, they all turned sharply round, the owner of the lantern throwing its rays full on the window outside which they were standing. The watchers drew back, in time evidently to escape detection, for the absence of footsteps and the recurrence, after a moment, of the curious sounds which Stanley had noticed from the smoking-room, assured him that they had once more returned to their work. The lantern, however, though it had failed to discover them, had, for a brief second, illumined the faces of the intruders, and both the Secretary and Madame Darcy recognised the trio. The man at work on the door was the Colonel; his assistants were Mr. Riddle and Miss Fitzgerald. The Secretary's worst suspicions were confirmed, and a smothered sob at his side told him that the discovery had inflicted no less keen a pang on his companion. She slipped down in a little heap on the ground, and he dropped on his knees beside her, whispering such consolation as he could without running the risk of being overheard. "I knew it must be so," she said, "and yet I hoped against hope that he was not guilty of this last infamy."