“It is not amongst the books you found in the underground room?” said Puttler, and a search was made of the library, but without success. They were on their way to the ruins when Puttler saw the aëroplane in the sky. It circled twice and then began to dip steeply. “I believe that fellow is coming here,” he said. And so it proved. The machine roared its progress for a hundred yards or more, and then dropped. Presently they saw a man get down. Though he wore an airman’s helmet, Dick recognized him. It was Arthur Gwyn. He met Gilder’s scowl with a little laugh. “I’ve got some money of yours, Gilder,” he said, and dragged with some difficulty a huge packet from the pocket of his leather coat. “That is more or less the amount I owe you, unless the franc has depreciated in value since I left Paris. And now you can do your damnedest!” Gilder took the packet without a word and Arthur turned to Dick Alford. “I read about Leslie in the French papers,” he said simply, “and so I came back. Has she been found?” Dick shook his head. “Have you any idea where she is?” Dick told him all that had happened that afternoon and Arthur Gwyn listened in silence. When Dick came to speak of his plan, he shook his head. “I had my early training as an engineer before I went into the law,” he said surprisingly, “and I tell you, from my elementary knowledge of the science, that you’re likely to blow in the whole well, and if there’s anybody on the other side, God help them!” He accompanied them to the lower room and was swung down on the derrick to make an inspection. When he returned to the surface his report was not very promising. “So far as I can see,” he said, “whilst you may enlarge the opening of any of these air holes, you may also bring about a fall of the rock inside. You’re dealing with surfaces which have been exposed to the chemical action of the air.” He went down and made an inspection of the lower room, which was new to him, and, as they had done, tried to pull the table aside. And then he did what they had not attempted; he pushed at the table at one end and felt it move, at first slowly and then quickly, as though he had set in motion a counterweight. He had just time to swing himself on the table and grip its edge when the aperture appeared under his feet. Dick saw the broken stair, and, sitting on the edge of the hole, dropped through to the rocky floor just as the table slid into its place. They pushed it back again and propped it, and Arthur and Gilder joined him below carrying lanterns. He saw a piece of something dark on the floor and picked it up. It was a strip of silk. “This is the way,” he said quietly. “I’ll work to the left; you go to the right, Gilder.” Arthur made a rapid mental calculation. “The left passage will lead you to the well, and unless I’m very much mistaken you will find the air holes on your right-hand side. If you don’t mind, I’ll go with you.”