And still it seemed as if he could hardly realize. “But someone must come,” he cried, angrily. “He can’t keep us shut in here for days.” She went across to him. “Didn’t you hear what he said as he went out? Suffocation. It took twelve hours for those two, and this is half the size. Six hours, Jack—six hours. And the servants are on the other side of the house.” And now at last he understood, and with the understanding he became himself again. He smiled thoughtfully, and pressed out his cigarette. “Under those circumstances—no smoking. And under those circumstances also—no scruples either.” He caught the girl in his arms and kissed her again and again, while she clung to him half sobbing. Then, still with the same thoughtful smile, he pushed her gently into the chair. “I must explore,” he said, briefly. First of all—the door. Coolly he examined it, while the girl watched him with eager eyes. He seemed so calm and assured—so completely confident in himself. A minute or two later he turned and looked at her. “Nothing doing there,” he said cheerfully. “It fits as tight as a safe door, and there isn’t even a keyhole on this side. It must have some patent form of lock.” He went round the walls quietly and systematically, tearing down the silk panels as he got to them. Nothing but smooth cement—not a crack, not a fissure. He stood on the desk to examine the roof. It was of flawless glass, immensely thick. And then he had to get down abruptly. He put his hand to his forehead; it was wet with perspiration. And now the full gravity of the situation had come home to him. Mad, Hubert Garling might be; there was no sign of madness about this trap. It was diabolically efficient. It was small consolation to know that the murderer might be hanged; all that mattered was that he and the girl he loved were in an air-tight room, and that in a few hours that air would be exhausted. He took off his shoe and hurled it with all his force at the glass above his head. For ten minutes he went on throwing it; then with a little gesture of despair he threw the shoe on the floor. The glass was too thick; he was only exhausting himself and using up precious oxygen uselessly. “Supposing we shouted, Jack?” said the girl, quietly. For a quarter of an hour they shouted “Help!” at intervals of half a minute. No one came; nothing happened. “It’s getting terribly stuffy, Jack,” she whispered. “Yes, darling; I’m afraid it is,” he answered, steadily. He was sitting on the arm of her chair—thinking desperately. Was there no way out? Was there nothing to be done? “He can’t mean to kill us like this,” she cried, in despair. He bent and kissed her gently, and she clung to him like a frightened child. And so they sat for twenty minutes or more, till suddenly the girl clutched his arm. “Jack,” she whispered, “look up. Oh, my God, look at him!”