The effect was amazing. The shafts of light from the machine's tube ceased; creamy liquid dribbled out from the cracked dome, and, as it met the air, frothed into billows of dense gray smoke. In seconds, the room was choked with a thick, foggy vapor that obscured every object in it as well as the blackest of moonless nights. * * * * * Istafiev had not fired again, could not. With a quick, frantic wrench and twist Chris had knocked the gun from his hand, and it had slithered away, now lost in the bunching smoke. But Istafiev's other hand, steel-ribbed with tense muscles, had darted like a snake into the American's throat, and under that iron, relentless grip Chris was weakening. His head was whirling; the old wound throbbing waves of nausea through him. Desperately he tried to struggle loose, flailing with his legs--but useless. He knew he was slipping; slipping.... Then, out of the gray, all-hiding mist, came a voice. "Istafiev! Where are you? Call! The machine's broken; I'm out and invisible. Where is the American?" Kashtanov! Istafiev hissed: "It iss all right. He will be finished in a moment. But you--go! The box iss aboard the plane; don't wait! You must not take chance of being hurt. Go to your work. Call Grigory in. Go, Kashtanov!" "I go, Istafiev." "No, you don't!" Chris Travers croaked almost inaudibly. "_You don't!_" Thought of the Canal lying there defenseless, of Kashtanov speeding towards it on his wrecker's errand, kindled within him a strength that was unnatural, superhuman. Like a wildcat he tore loose from the choking grip on his throat; Istafiev tried to subdue that sudden, unlooked-for surge of power, but could not. Five piston-like, jabbing blows crunched into him from Chris's hurtling fist, and with the fifth Istafiev faded quietly out of the picture.... Chris sprang up and started a leap for the door he could not see. A body brushed against him; dimly through the smoke he saw the man called Grigory, and Grigory saw him, but not for long. A whaling swing lifted him two inches clear of the floor, and then he went down onto the peacefully recumbent Istafiev; and Chris Travers, fighting mad, stormed from the hut into the clearing outside. The camouflaged framework had been raised; soft motors were purring helicopter propellers around and lifting a plane up towards the stars hanging high above. The airplane was already feet off the ground and sweeping straight up. A sane man wouldn't have thought of it, but Chris wasn't quite sane just then. With a short sprint, he launched himself into a flying leap, grabbed out desperately--and felt the bar of the undercarriage between his hands. The plane jolted. Then it steadied; rose with terrific acceleration. And Chris hauled himself up onto the undercarriage and clung to one of the wheel-stanchions, breathing, hard, hidden by the fuselage from the invisible pilot.