I interrupted impulsively, "Just tell me this. Does it, this thing, whatever it is--does it concern the ghosts?" I was aware of a shudder that ran over Bee. Will did not move. "Yes," he said. "It does. And these ghosts have changed. We knew they would--we've been expecting it." "That poor girl," Bee said softly. "Dead--dead in her bed of fright. You read about it, Rob?" "A menace," Will went on. "The world is just realizing it now. Ghosts, changing from shadow to substance--" He stopped, then added abruptly, "We've never told you much about our work--our business--have we?" They had in truth always been reticent. I had never been in their laboratory. They were engaged, I understood, chiefly with soil analysis; sometimes people would come out to consult them. Beyond such a meager idea I knew nothing about it. Will said abruptly, "Our real work we have never told anyone. It concerns--well, a research into realms of chemistry and physics unknown. I have been delving into it for nearly ten years, and then Bee grew old enough to help me. We've made progress--" His smile was very queer. "Tonight--I'm ready to show you something that I can do." They seemed to torture Bee, these words of her brother's. I heard the sharp intake of her breath, saw her white fingers locked tensely in her lap. "Not--not tonight, Will." "Tonight--as good a night as any other.... Rob, would it surprise you to know we anticipated the coming of the ghosts years ago? Not that they would come, but the possibility of it. Ghosts! What do you think they are, Rob?" "Why ghosts--ghosts are--" "Spirits of the dead made visible?" His manner was suddenly vehement; his tone contemptuous. "Earth-bound spirits! Astral bodies housing souls whose human bodies are in their graves! Rubbish! These are not that sort of ghosts." I stammered, "But then--what are they?" "Call them ghosts, the word is as good as any other." His voice grew calmer; he went on earnestly, "I want you to understand me--it's necessary--and yet I must not be too technical with you. Let me ask you this--you'll see in a moment that none of this is irrelevant. How many dimensions has a point?" At my puzzled look he smiled. "I'd better not question you, Rob, but you won't find me hard to understand. A point--an infinitesimal point in space--has no dimension. It has only location. That's clear, isn't it? A line has one dimension--length. A plane surface has length and breadth; a cube, length, breadth and thickness. The world of the cube, Rob, is the world we think we live in--the world of three dimensions. You've heard of that intangible something they call the fourth dimension? We think it does not concern us--but it does. We ourselves have four dimensions. We are the world of the fourth dimension. But the fourth is not so readily understood as the other three."