"Also cracks," grinned Gary, "about Kang's charming daughter, Pen-N'hi. Which Lark doesn't allow. But, no, Mac; I'm sure you're mistaken. As soon as we reach the asteroid belt Dr. Kang has promised us proof that the force-shield has been installed and is in operation." With this assurance everyone had to be content, until ten days out from Mars the _Liberty_ hove within range of that tremendous swarm of shuttling bodies which comprises the Bog, spaceman's term for the belt of myriad asteroids ranging in size from tiny granules of rock to life-sustaining mountains of matter larger than many satellites. * * * * * It was when they reached this point that Dr. Kang offered his promised proof. As the leaders of the party gathered within the _Liberty's_ control turret he said, "And now, for those of you who have not had the opportunity of seeing the Martian force-shield operate, a little demonstration may be heartening. Who's at the controls? O'Day? Good! Larkspur, my friend ... you see that asteroid moving within our vision range to loft and starboard?" O'Day, fingers flickering incessantly over the keyboard as the ship wove its way through the treacherous belt, nodded tightly. "I see it," he grunted, "and I'm getting out of its way now. If that thing ever plowed into us, the _Liberty_ would be one small blob of crumpled metal floating through space." "On the contrary," said Dr. Kang smoothly, "you will make no attempt to avoid the planetoid. You will set a course directly for it." "Directly--!" gulped Lark. "Yes. If you will be so kind." Then Dr. Kang stepped to the board and depressed the single black stud he had installed on the instrument panel. "Steer directly for that rock at the greatest speed you can achieve." O'Day essayed a grin that didn't quite jell. But with the eyes of Pen-N'hi upon him, he had no intention of showing the white feather. He merely shrugged. "You're calling signals," he muttered ... and did as the old Martian directed. With the die irrevocably cast, young Dr. Lane could sympathize completely with the _Liberty's_ pilot. He, too, felt qualms of misgiving as the cruiser bore down at flashing speed upon a chunk of rock large enough to shatter the ship into billions of tortured rivets. Nor was it pleasant to stare into the viewpane, watching that lethal asteroid loom ever larger and more deadly, now like a gray, grim, gaunt and fearsome stony beast, its gaping canyons yawned like fangs bared to destroy them. Nearer and nearer flashed the _Liberty_. Lane's heart missed a beat ... then another ... then started pounding with an excitement which moistened the palms of his hands and dried his lips. He cast a nervous glance at Dr. Kang. But the aged Martian's features were expressionless. Flick Muldoon was frankly apprehensive, and Nora Powell, standing next to Warren across the room, moved closer to the sturdy space captain as though to eke from his presence some breath of reassurance.