Torcred slammed down one foot pedal and the terrapin slewed crazily and slid sidewise for a score of yards, in a cloud of sand that momentarily hid it from the eyes above. Coming out of the skid he gave full power to the spinning wheels, operating the throttle with one hand while the other switched on his radar screen and leaped from it to the firing control of the turret gun. It was long seconds before the scanning beam located its flitting target; then, though the terrapin was traveling in the quick swerves and dashes of a desperately evasive course, the automatic control held the image reasonably well centered on the projected crosshairs of the turret gun's sight. The image swelled, grew wings, as the aero came in in a second howling dive. Torcred's reflexes, hardly less automatic than his machine's, depressed the firing button, and the gun's stammering blast numbed his ears, mingling almost at the same moment with the clang and shriek of steel on steel as the terrapin took more hits. But the flying enemy leveled off far higher than before and zoomed away more steeply; its great advantage had been lost when the first attack failed to cripple or kill. The Terrapin's eyes burned into the screen as his own wild zigzags flung him painfully against his safety belt. The aero might let things go at that.... No, the screen's image expanded again. His finger closed once more on the firing button. The winged outline grew with ominous determination. Careless now of the single gun that rattled defiance, it was coming down for the kill. With the corner of his eye Torcred saw the vicious puffs of sand that strode to meet the racing terrapin; he swerved instantly, but in that same instant the car staggered and spun out of control. He did not hear the thunderous concussion that stung his face and hands. The forepart of the roof bowed inward, and there was a knife-like fragment of steel, inches long, in the cushion almost touching Torcred's ear. Dimly he realized that his wheels were spinning futilely, the car canted far over; it had nosed into a dune and half-buried itself. The fight was over.... But ten, twenty seconds went by and no fresh storm of destruction burst on him. Incredulously his eyes found the radar screen. It was still working, and the image that filled it wavered strangely, neither receding nor coming nearer. He threw his machine into reverse and opened the throttle; the front wheels took hold and the terrapin bucked itself free of the sand. Then Torcred leaned sidewise, recklessly flung open a steel shutter and looked out. He blinked, dazzled, at the sweep of desert and bright blue sky before his eyes found the falling shape, twisting and fluttering as it fell despite its weight of tons. As he watched, the aero almost leveled out, teetered on one wing and sideslipped out of sight behind a distant dune. A cloud of dust sprang up and drifted away, but no smoky death-pall rose after it. * * * * *