Meanwhile, Mortenson, with five expert opticians and three master mechanics under him, worked doggedly in his laboratory. The laboratory adjoined the scientist's big house where they consumed their meals hurriedly. Mortenson slept with the men a few hours each night in the workroom. Plain-clothes men lurked about the place as a precaution against a raid on the scientist by the vanishing criminal who, they suspicioned, might have learned through the grapevine system what was going on. But the crook appeared to have taken Mortenson's word that it was impossible to duplicate the instrument that transferred him from one plane to another. He seemed satisfied to add to his already fabulous coffers and let the scientist alone. Perhaps he was afraid of Mortenson, fearing that the scientist might have evolved some means of nullifying the effect of the vibration on the physical body. Mortenson was elated at his progress, but he had a constant fear of the criminal. Doubtlessly the man would kill him if he learned that he was putting his heart and soul into the work of building sufficient apparatus to outfit a squad of police officers who would use them to hunt him down in the mysterious, invisible world. Yet the scientist worked dauntlessly, night and day, feeling more secure with each passing hour as the instruments neared completion. To kill Mortenson, the desperado would first have to emerge from behind the veil of the Fifth Dimension. To do this would lay him open for immediate death at the hands of the officers and plain-clothes men, who constantly guarded the scientist. As a further precaution, Mortenson was on the alert at all times. He was armed and ready to defend his life, yet there persisted within him a constant fear that the man would unexpectedly appear and shoot him in the back. Finally Mortenson stepped back and appraised ten complete Fifth Dimension sets neatly arranged on the workbench. Each set was equipped with a wide metal belt, attached to which was a small, oval box containing storage batteries capable of releasing vibratory electronic current. Loose wires as thin as thread, with small plugs at the ends, ran from the head-gear. The gear appeared like field glasses connected to a leather helmet. But inside the leather ran meshed wire with bare electrodes exposed to fit snugly against the forehead and the back of the neck. He trembled with excitement when he realized that at last the job was completed. The plans had been followed to the minutest detail. Nothing could go wrong and Mortenson shivered at the thought of what lay behind the curtain that hid the Fifth Dimension from view. He meditated a moment on the miracle that had prevented the phantom terror from meeting his doom behind the veil. Then his telephone disrupted his thoughts. He went to it at once. His caller was Chief Steckel and his voice trembled fearfully.