Dan tore down the stairs and across the catwalk two steps ahead of Rawlins. He hammered on the door. Through the thick glass he could see Stevens hunched over the lighted control table. "Stevens! Stevens!" He turned to Rawlins. "We'll have to cut the lock. Get a torch--and get a doctor!" It took a minute with a high torch before they crashed into the room. "He's been dead several minutes," the doctor said as he took his hand from Steven's forehead. "I'm sorry, Kearns," Rawlins said. He looked at the doctor. "Well, I guess that explains everything. He must have lost control just as she was coming in. What was it? Heart attack?" The doctor shook his head. "Some sort of convulsion. Muscles violently contracted. Funny he didn't fall to the floor. Must have affected the whole nervous system. Even the eye pupils are down to pin points." He looked around at Rawlins. "I may be sticking my neck out, sir, but off hand I'd say Stevens was killed." "Killed?" Rawlins blinked at the form in the chair. "But that's impossible. The door was locked. The room hasn't been disturbed and there aren't any holes in the glass. Nothing could get in here except light." Dan walked to the big windows. He examined the ledge and the joints. He came back to the control table and tested the switches. Suddenly he leaned over Stevens' huddled body and pulled the log book from under his stiff fingers. "Look at this!" Scrawled across the pad in big jerky letters were the words "_Purple light bea_...." The pencil had torn through the sheet in a violent final contraction. Rawlins rubbed his chin. "We don't use any purple beams. It doesn't make sense." "Maybe it does," Dan said. He turned to the doctor. "Wasn't there some experiments made by a Dr. Aren Linden several years ago on the injurious effect of certain kinds of light on the nervous system?" The doctor frowned. "Yes, I think there was, but the experiments were never completed." "That's right. The foundation refused to up his salary, so he went to work for Roehm." Dan swung around to Rawlins. "It was Linden who helped work out the invisible light landing system that Roehm uses on his Venus rocket ports." "Seems to me you're jumping to some pretty wild conclusions, Kearns," Rawlins said slowly. Dan looked at him. "Suppose Linden has found the exact wave-length of the most potent ray. It would be simple for anyone to climb the framework of one of the buildings and shine that light in here." Rawlins straightened up. "I'll search every tower on the field." "But you haven't time. That passenger rocket will be here in five minutes." The supervisor sucked in his breath. "What's your idea?" "I'll sit at the control table myself. You can do the preliminary locating in the observation tower." He ran to the door. "Where's the welder that cut the lock?" * * * * *