"This Gray, though, knew all about your projector just finished, something but a handful of people did. And since he had seen it make a man perfectly invisible, he must have been aware what powers its possession would give anyone who wanted to go in for criminal activities?" "Anyone would have been aware of that," Dr. Grantham rejoined. "President Ellsworth remarked on it at our demonstration yesterday." "You cannot say, however, that it is impossible that Gray, after leaving, crept back into the laboratory and struck you down and took the projector?" Wade pursued. Gray Did Not Return Dr. Grantham considered. "No," he said slowly, "but I would say that it sounds impossible to anyone who knew Gray." Wade was silent, apparently revolving something in his mind, but before he could ask another question there entered the officer he had sent below, who spoke to him briefly in low tones. When he had done, Wade turned again to the physicist. "How is it, then, that Gray did not return to his rooms when he left here, and has not been seen there since he left yesterday morning.” "Good Lord!" Carton burst in excitedly. "Then it's Gray that--" Dr. Grantham's face showed his astonishment and trouble. "Gray was not a criminal type," he persisted. "I simply cannot believe that it was he. More likely by far some thief who found the building's door open and who, seeing me about to lock up the projector, struck me down to get it." "Well, Gray or another," Wade remarked, "someone is loose in New York at this moment with a thing which, if you're right, can give him the power to walk its streets unseen." "But you'll endeavor to catch him?" President Ellsworth interposed anxiously. "I know but little about Grantham's mechanism, but surely it will be a terrible threat until whoever has it is captured?" "We'll do what we can," Wade told him gloomily. "But it's going to be pretty hard to keep the force looking for someone they can't see! Even if they believe in the story at all. But I wouldn't worry about the thing, sir--visible or invisible, a crook can only keep free so long when thousands are concentrating on finding him." "I sincerely hope you're right," said President Ellsworth as he turned to the door, hat in hand. "I'll see you tomorrow about it, Grantham--and take care of yourself until then." When he had gone Dr. Grantham said quietly, "I am glad that he does not fully realize the appalling nature of this thing. I did not want to worry him to no purpose. Whether it was Gray who took the projector or another, is really immaterial now. The fact, the great fact, is that someone has it who has proved himself ruthless. And with it, he can loose such a terror upon New York--yes and upon the nation--as might be utterly without precedent!" "One man?" asked Wade, skeptically.