So that was it! The combination of gruelling labor in the effort to save mankind from the dread moon weed, and bitter censure from the very people he was trying to save, had been too much for Van. He had developed a fixation, unreasoning and murderous; he'd get even with the man who had caused the trouble. And nothing could deter him from his purpose: Bart could see that. Might as well humor him and help him. It made little difference, anyway, with the red doom spreading at its present rate. They'd all be victims in a few days. They were speeding through the streets of Washington at a break-neck rate. Van bent over the wheel, and like a demented man glued his wildly staring eyes to the road. "What about your work?" Bart asked, after a while. "Has anything been accomplished?" "Yes and no. They'll be ready to shoot in a few hours. Don't know whether it'll be a complete success or not. But I sneaked away anyhow. This other thing's more important to me right now." "What's the dope? Can you tell us now?" "Sure. I've got one of the machines in the car and I'll explain when we're on our way to Canada." This wasn't like Van. Never secretive and always in good humor, he was treating his friends like annoying strangers. "You can't land in Canada," Bill ventured, as they pulled up at the gate of the airport. "Like hell I can't! You watch my smoke, and let any bloody Canuck up there try and stop me!" He was lifting a small black case from the luggage carrier of the car as he replied. Bart silenced the airman with a look. * * * * * When they had taken off and were well under way, Van opened his black case and set a vacuum-tube apparatus in operation. They were nearing the fringe of the glowing sea of red that was the vast blanket of moon weed. It now extended to within a few miles of Baltimore and stretched northward as far as the eye could see. "It was a cinch," Van was explaining. "When I first saw that the growth slowed up under the arc-lights at Tomkins Cove it gave me the glimmering of an idea. Then, on the following day, when we learned that the weed spread more slowly in sunlight, I was convinced. The stuff is dormant on the moon, you know." "Why?" Bart asked breathlessly. "Because there is no atmosphere surrounding the moon, and the sun's rays are not filtered before they reach its surface as they are here. The invisible rays, ultra-violet and such, are present in full proportion. And the moon weed can not flourish when subjected to light of the higher frequencies. It died out when the moon lost its atmosphere, and only revived on being brought to earth--probably a million times more prolific in our dense and damp atmosphere and rich soil. The thing's a cinch to dope out." "Yeah!" Bart commented drily. Van was now talking and he could have bitten off his tongue for interrupting him.