They carefully avoided the partially invisible robot, for the humming of its upper motors continued and clanking sounds occasionally issued from the unseen upper portion. The enemies of David Shelton were still at work on their hidden controls. "Here--what's this?" Eddie exclaimed suddenly, pointing out a glinting object in a dark corner of the laboratory. Shelton examined it closely, looking over his shoulder. The object he had located seemed to be a mounted and hooded lens, a highly polished glass of about two inches diameter with its mounting attached rigidly to the wall. "Never saw that before," Shelton stated with conviction. "And--why--it looks like an objective such as those used in the latest automatic television transmitters." "Just what it is," Eddie grunted. He picked up a pinch bar from a nearby tool rack and drove its end through the glass as he spoke the words. A violent wrench tore the thing loose and broke away a section of the thin plastered wall. There, in the cleverly concealed cavity behind, was revealed the mechanism of the radio "eye." Somewhere, someone bad been watching their every move. And abruptly the thrashings of the robot ceased and its upper portion again became visible. * * * * * "Well," said David Shelton. "Well! Looks as if you're right, young man. I'm astonished." His watery eyes looked sheepishly over the rims of his glasses. Lina watched their every move. She seemed to sense the seriousness of the situation far more than did her father. Then the lights went out. It had darkened to night outside and the blackness and silence in the laboratory was like that of a tomb. "They've cut the wires," Eddie whispered hoarsely. "Got any weapons here, Shelton?" "Yes. A couple of automatics. I'll get them." The scientist was no coward, anyway. His whispered words came calmly through the silence. Eddie heard him shuffle a few steps and fumble with a drawer of the desk. In a moment the cold hard butt of a pistol was thrust into his hand. It had a comforting feel. "Stay here with Lina," he commanded. "I'll go out and see if I can find them. This looks nasty to me." "No," came the girl's voice, "I'm going too." "You are not," Eddie hissed. "You'll stay here or I'll know the reason. It's dark as a pocket outside and my eyes are as good as theirs. I'll get 'em if they're around here. You hear me?" "Yes," she whispered meekly. Edward Vail, only that morning headed for rest and quiet, was now out in the night, stalking an unknown and vicious enemy. And--for what? As he asked himself the question, the smile of Lina seemed to answer him from the blackness. Cherchez la femme! He was getting dotty as he neared his thirties. Maybe it was the hard work that had affected his mind. * * * * *