With a smothered curse, Elijah Callister drew back into the room. "Fooled again!" he muttered, fiercely. "If the builders of this infernal den had constructed that place on purpose to raise my hopes, they could not have succeeded better. We'll have to try again." The words had scarcely left his lips, when from the gloom behind them a strange sound fell upon their ears. It was half-sigh--half-groan. It seemed to come from behind the bed. "My God! Lije, did you hear that?" exclaimed Tisdale, in a hoarse whisper, seizing his companion by the arm. At the same instant from behind the bed there emerged the form of a woman, tall and thin, with pinched features, wild, restless eyes, and long gray hair hanging down her neck and shoulders. Coarse, worn garments hung loosely about her, a cheap shawl was thrown carelessly about the shoulders and pinned across her breast. With one long, white finger extended before her, she advanced slowly toward the villainous pair without uttering a word. Could Frank Mansfield have seen her, he would have instantly recognized the mother whose death he mourned. Could Detective Hook have seen her, not for one instant could he have doubted that Mrs. Marley, whose dead body he had raised with his own hands from the floor of that wretched upper chamber in the rear of the Donegal Shades, and this woman were one and the same. With a cry of horror Reuben Tisdale sprang backward toward the fire-place. "Keep back, woman!" he yelled, his eyes starting from his head in terror. "God have mercy! 'Tis the spirit of my murdered wife!" With a deep sigh the specter, with a gliding motion, moved backward, disappearing in the gloom beyond. And even as the last glimpse of her shadowy form had disappeared from the gaze of Elijah Callister, who, with whitened face, stood still, grasping the lantern in his hand, his companion fell forward with a deep groan, motionless upon the floor. CHAPTER XVII. AN ADVERTISEMENT. When Frank Mansfield awoke next morning he found Detective Hook standing by his side. Indeed, it was the pressure of the detective's hand upon his forehead that had called him from sleep. "Good-morning, my boy," he said, pleasantly. "It's time you were stirring, if you intend taking breakfast with me." Frank sprang off of the lounge and began putting on his clothes. "I could sleep all day, I think," he said, rubbing his eyes. "I never felt so sleepy in my life." "No wonder, after the strain you have been under for the last forty-eight hours. That was one reason why I insisted upon your coming home with me. I want you to get thoroughly rested and refreshed; then you will be able to show what you are made of in working out our scheme. That hole in the wall may do well enough for newsboys and bootblacks, but it is no place for a boy like you." "It served me a good turn the other night, all the same."