As they stood in the empty ballroom, its walls lined with age-old portraits, the furniture dusty and moth-eaten, there came a sound that made even Cleek, to whom it was no stranger, shudder. It was a low, horrible moaning which seemed to permeate the whole house. For a moment they stood rooted to the spot in horrified silence, then Sir Edgar spoke in a quaking whisper: "Heavens above! what is it?" Nobody answered him, for it was a question impossible to answer. All they could do was to search the house again from garret to basement, but Miss Cheyne had apparently disappeared as mysteriously as her niece. Whether by her own will or not, it was impossible to say. Back once more on the terrace they were compelled to own themselves beaten, and Cleek and Mr. Narkom looked at one another in sympathetic dismay at this set-back to their plans. They both had counted on coming face to face with the eccentric guardian of the girl whose life was in such evident danger. Suddenly Sir Edgar gave a little startled exclamation and turning in the direction of his gaze they saw the figure of a fair and slender woman running toward them. As she drew near, Cleek's heart gave a little leap of delight, for it was the woman who meant more to him than all the world. A second later he quickened his steps to meet her. "Oh, I am so worried!" Ailsa said swiftly. "I am thankful I have found you at last. It is that poor girl you drove home that night, Lady Margaret Cheyne, you know. I have tried so many times to see her. I have called and called, but have always been refused admittance. Now this morning I was in the lane when I saw Lady Margaret at a window and she dropped this scrap of paper. See!" She handed Cleek a little screwed-up piece of paper on which was scrawled "Miss Lorne, save me! Margaret." "She was snatched away before I could call to her. What does it mean?" asked Ailsa, wistfully looking from one face to the other. "I should not be surprised if that dangerous stone, the Purple Emperor, is at the bottom of it all," said Cleek. Sir Edgar took the scrap of paper from Ailsa's fingers, and read it slowly through. Then he cried vehemently: "I'll save her, if I commit murder fifty times over." As he spoke, he plunged along the lane, the ill-fated words lingering in their minds long after he had disappeared. "It's an absolute mystery at present," said Cleek softly, his chin pinched up in his hand. "There must be some way of getting in and out of that house which we haven't yet fathomed, and I'd like to have a shot at finding it. I think, too, we shall have to keep an eye on our young friend, Sir Edgar, or he will be getting into trouble. Never fear, Ailsa," he added, gently, "I will save the little girl somehow, but I mean to give myself the pleasure of walking back with you first."