The two men were on the brink of success. Then there was an abrupt, strident, angry, snap from the vitals of the Penetrator apparatus. Everything seemed to happen at once. The protecting blue aura outside the ship waxed and waned perilously. And whenever it waned, there was a grinding, crumpling sound, as of steel plating being crushed like so much paper in a giant's grip. Heat, and the cindery pungence of scorched metal, filled the cabin. Paul Arnold and Evan Harwich were frozen rigid with stunning, agonized paralysis, as strange energy snapped into their bodies. In the jolting, erratic motion of the wounded space ship, the two men were hurled from their feet like a pair of stiff wooden dolls. Rolling and tumbling, his vision half blinded, Harwich saw the metal walls of the cabin buckle and redden with heat, as the craft floundered in that region of mysterious force and energy that heretofore had destroyed every ship that had attempted to reach Io. There was another growl from the protecting apparatus. In a flash of electricity, the side of the bakelite case that housed the Gyon condenser exploded outward. At once the staggering Penetrator quit completely. Its last shred of protecting force was gone. But that momentary hell had ended, too, with almost dazing suddenness. The grinding, snapping sounds had ceased. And there was only the heat and the stench of burnt metal, and the weightless sensation of free fall. That and the mocking stars. Paul Arnold, panting, his face darkened and beaded with perspiration, clutched a bakelite handrail in one corner. "We got through Io's energy barrage!" he shouted wildly. "We did that much, at least; and for a moment, when our Penetrator went wrong, I didn't think our luck would be even that good." Evan Harwich leered back at the youth, from near the now useless apparatus that John Arnold had invented. "Yes, we got through," he grunted hoarsely. "The energy shell must be only a couple of thousand miles thick, with free space underneath, between it and Io itself. The Gyon condenser kept working raggedly just long enough to get us out of the danger zone, without being completely blown apart!" Harwich didn't have to test the controls of the ship to know that they were useless, now. The rockets were silent too. The RQ257 was falling free toward the Forbidden Moon, still a couple of thousand miles beneath. "But dammit, Evan!" young Arnold growled. "The Gyon condenser shouldn't have quit on us at all! Those things are tested for heavy loads of power!" The patrol pilot was well aware of that. Clinging to the base of the Penetrator, he was close enough to see detail. The lights in the cabin had gone out, but the ugly effulgence of Io was streaming through the windows. Projecting from the shattered bakelite box of the Gyon condenser, were two slender, bent wires that should have been joined together. It had been one wire once, but it had snapped in the middle.