Knebworth had already taken the girl off in his car to Chichester, for she had shown signs of reviving, and he wanted to get her away from that house of the dead before she fully recovered. Michael went down into the cave again and joined the inspector. Together they made a brief tour. The headless figures in the niches told their own story. Farther on, Michael came to the bigger cavern, with its floor littered with bones. “Here is confirmation of the old legend,” he said in a hushed voice, and pointed. “These are the bones of those warriors and squires who were trapped in the cave by a landslide. You can see the horses’ skeletons quite plainly.” How had Adele got into the cave? He was not long before he found the slide down which she had tumbled. “Another mystery is explained,” he said. “Griff Tower was obviously built by the Romans to prevent cattle and men from falling through into the cave. Incidentally, it has served as an excellent ventilator, and I have no doubt the old man had this way prepared, both as a hiding-place for the people he had killed and as a way of escape.” He saw a candle-lantern and matches that the girl had missed, and this he regarded as conclusive proof that his view was right. They came back to the guillotine with its ghastly burden, and Michael stood in silence for a long time, looking at the still figure stretched on the platform, its hands still clutching the sides. “How did he persuade these people to come to their death?” asked the inspector in a voice little above a whisper. “That is a question for the psychologist,” said Michael at last. “There is no doubt that he got into touch with many men who were contemplating suicide but shrank from the act, and performed this service for them. I should imagine his practice of leaving around their heads for identification arose out of some poor wretch’s desire that his wife and family should secure his insurance. “He worked with extraordinary cunning. The letters, as you know, went to a house of call and were collected by an old woman, who posted them to a second address, whence they were put in prepared envelopes and posted, ostensibly to London. I discovered that the envelopes were kept in a specially light-proof box, and that the unknown advertiser had stipulated that they should not be taken out of that box until they were ready for posting. An hour after those letters were put in the mail the address faded and became invisible, and another appeared.” “Vanishing ink?” Mike nodded. “It is a trick that criminals frequently employ. The new address, of course, was Dower House. Put out the lights and let us go up.” Three lamps were extinguished, and the detective looked round fearfully at the shadows. “I think we’ll leave this down here,” he said. “I think we will,” said Michael, in complete agreement. CHAPTER XLII CAMERA!