He went up to the apparition of a door, abruptly seemed to melt into it. Barney held his breath, and followed. Again there was no sensory reaction to passing through the Tube. As his foot came down on something solid in the shadowiness into which he stepped, the living room in Sweetwater Beach sprang into sudden existence about him. "Seems a little odd from that end, the first time through, doesn't it?" McAllen remarked. Barney let out his breath. "If I'd been the one who invented the Tube," he said honestly, "I'd never have had the nerve to try it." McAllen grinned. "Tell you the truth, I did need a drink or two the first time. But it's dead-safe if you know just what you're doing." Which was not, Barney felt, too reassuring. He looked back. The door through which they had come was the one by which they had left. But beyond it now lay a section of the entrance hall of the Sweetwater Beach house. "Don't let that fool you," said McAllen, following his gaze. "If you tried to go out into the hall at the moment, you'd find yourself right back in the cabin. Light rays passing through the Tube can be shunted off and on." He went over to the door, closed and locked it, dropping the key in his pocket. "I keep it locked. I don't often have visitors, but if I had one while the door was open it could be embarrassing." "What about the other end?" Barney asked. "The door appeared in the cabin when you turned those switches. What happens now? Suppose someone breaks into the cabin and starts prowling around--is the door still there?" McAllen shook his head. "Not unless that someone happened to break in within the next half-minute." He considered. "Let's put it this way. The Tube's permanently centered on its two exit points, but the effect ordinarily is dissipated over half a mile of the neighborhood at the other end. For practical purposes there is no useful effect. When I'm going to go through, I bring the exit end down to a focus point ... does that make sense? Very well. It remains focused for around sixty or ninety seconds, depending on how I set it; then it expands again." He nodded at the locked door. "In the cabin, that's disappeared by now. Walk through the space where it's been, and you'll notice nothing unusual. Clear?" Barney hesitated. "And if that door were still open here, and somebody attempted to step through after the exit end had expanded--" "Well," McAllen said, moving over to a wall buzzer and pressing it, "that's what I meant when I said it could be embarrassing. He'd get expanded too--disastrously. Could you use a drink, Mr. Chard? I know I want one." * * * * *