"Destroy the _Selba_!" Shelby exploded, "with what? Those toy machine guns on the nose of this bus? The bullets wouldn't even make noticeable scratches in the hide of that tough old girl." "Not with the machine guns," Jan said slowly, "with this flier! A little luck and it would work." The idea flashed through Shelby's brain. Ram the _Selba_ at high speed! Absolutely certain self-murder! A wave of tremendous admiration for the girl came over him. She had something more in her favor than mere beauty and intelligence. "Your idea is a pretty good one, Jan," he told her. "But rest assured that unless you can overpower me, it will never be put into execution. However, I'll tell you the truth: we have about a fifty-fifty chance of reaching the Red Planet alive." And so they tore on their way across the void while they watched the dial on the oxygen tank. They were racing with a tiny needle that crept ever nearer to the zero point that was its goal. By allowing the pressure within the flier to drop to the lowest point that they could endure, they managed to conserve considerable oxygen, for then the rate of escape from the crevice the torpedo fragment had made was naturally not so rapid. Frequently they examined the sky behind them, expecting momentarily to discover the tiny speck of flitting silver that would be the _Selba_. But if the ship was pursuing them it had not yet come close enough to be seen. However, there was another, and perhaps greater menace which kept their eyes turning this way and that, searching for signs of danger. Clusters of dully-glowing specks in any quarter of the heavens would be the first indications of its presence. They would grow larger, come hurtling on like racing meteors in the sun's glow. Only there would be an odd wobbly motion about their darting flight. Shelby tested the trips of the two machine guns. Spurts of green flame plumed out of the muzzles. He had set the radio transmitter in operation, and was sending occasional signals for assistance. But he knew that this was practically a useless move. Hekalu had taken them far off the beaten track, and they were still half a million miles from the Terrestro-Martian traffic lane. The range of the transmitter of this craft was only ten thousand miles. Even if they had been much nearer the chances of their signals being picked up were slight. The Martian disc was growing larger. It had become an ochre sphere delicately ringed and mottled with greens and browns like a cloudy opal. The flier was fairly eating up the distance. Shelby had just said: "I believe we're going to make it, Jan," and then the signs which they had hoped would not appear came. Ahead of them and a little to their right, a vague cluster of specks glimmered into view. It wavered like a wisp of luminous smoke buffeted by a light breeze. This was the one thing that distinguished it from a meteor cluster. * * * * *