This machine of Van's was a generator of invisible light in the ultra-indigo range, Van explained. You couldn't see its powerful beam, but they had proved in the laboratory that it was certain doom to the moon weed. They had grown the stuff from seed in steel cages, and played with it until they were all satisfied. Now would come the final test. Ten thousand planes were being equipped with the new generator, which was merely an adaptation of standard directional television transmitters, and to-night these would start out to fight the weed. It was a cinch! * * * * * Beneath them the red cauldron seethed and tossed as they sped northward; the crimson blanket of death that was steadily covering the country. "Drop to a thousand feet, Bill," the scientist called, "and then watch below. But, don't slow down. We've got to get to Toronto!" The ship nosed down and soon leveled off at the prescribed altitude. Van's vacuum tubes lighted to full brilliancy, and a black spot appeared on the glowing surface just beneath them, a black spot that extended into a streak as the plane continued on its way. They were cutting a swath of blackness fifty feet wide through the heart of the growth! "See that!" Van gloated. "It's killing them by millions! And the best of it is the effect it leaves behind. The soil is permeated to a depth of several inches and the stuff will not germinate in the spots where the ray has contracted. Oh, it works to perfection!" Bill was exuberant; his hopes revived miraculously. He gave his motor the gun and got out of it every last revolution that it could turn up. He must get Van to Canada! Not such a bad idea, this going after Kelly, at that! Bart was voluble in his praise, then caught himself short as he remembered that he had doubted Van but a half hour previously: doubted him and despaired. Now Van, lapsing into gloomy silence after his triumph, was again thinking of nothing but revenge. The getting of Dan Kelly meant more to him now than the extinction of the moon weed. * * * * * When they landed at the Toronto Airport they were welcomed with open arms instead of with rifle fire as Bill had anticipated. The news had gone forth. Already a thousand planes flying over the United States were driving back the sea of destruction. The invisible ray was a success, and the name of Carl Vanderventer was now a thing with which to conjure, rather than one on which to heap imprecation and insult. Van grimaced wryly at this last bit of news. Danny Kelly? No one at the airport had ever heard of him. Van telephoned in to the city; to Police Headquarters. Yes, they had apprehended the fugitive American at the request of Washington, but he was a slippery customer. He had escaped. Van raged and fumed.