"That's easy, Barton," said Mortenson coolly. "I was lying right there on the floor, knocked out completely. As usual I worked late last night. About midnight a masked man came in here, robbed me of my Fifth Dimensional apparatus, knocked me cold with his gun and skipped. That's the reason for the bandages on my head and the cause for that blood-stain on the floor near your feet. I came too about an hour ago, had Doctor Brandon sew me up, and then bought a newspaper which informed me of the bank holdup and killing. "I hardly blame you for suspecting me, but you can see at a glance that I had nothing to do with the bank affair, except, of course, giving the crook instructions as to how to operate the apparatus." "Why did you do that?" snapped Barton. "To live, Barton," the scientist retorted. "You probably know what it is to face a gun, not knowing what minute it might go off." The detectives exchanged baffled glances and Barton bent over to appraise the blood-stain on the floor. Riley's eyes roved about the room and finally concentrated on Mortenson's bandaged head. "Suppose we have a look at that head, Mortenson," he said with a shrug of his powerful shoulders. Barton looked up. "Never mind that, Riley," he said authoritively. "Let Wagner do that at headquarters." "You mean you are going to take me in on suspicion?" Mortenson sat bolt upright. "I've got a warrant for your arrest, Mortenson," the other replied firmly. "Your story sounds pretty good to me, but I'll have to book you at least. You'll probably be released on your own recognizance, if the police surgeon's report is satisfactory. You know...." "Oh, I know, Barton," said the scientist with a nod. "You think I might have put that stain there and bashed my own head to establish an alibi. Well, you're all wrong. Look in the wash-stand and you will see that I washed the blood off my head and face there. It takes at least eight hours for blood to coagulate and I'm sure you will find clots in the sink to prove that I was injured shortly after midnight." "Why didn't you report to headquarters when you came to?" Riley grumbled. "I don't know," said Mortenson. "I guess I was too dazed. Then Dr. Brandon came and fixed me up. After that I became interested in the news of the bank robbery." III _Mortenson Explains_ Entangled in the net of the law, Mortenson, despite his high social standing and fame as a scientist, was taken to police headquarters and summarily booked on suspicion. He went through the process of being finger-printed and "mugged" like a man in a trance. All the while his head ached violently, sending sharp, stabbing pains through his brain. The reaction of the blow was telling on him now and his hands shook. But he submitted to the rigid rules of the police department without protest, for he had little fear of failure in proving his innocence, if given the chance.