the ringwall was not very large. slowed by his vac-suit, a man might cover its diameter in half an hour. but steve did not traverse the circular area. instead, he climbed the ringwall laboriously and then made his way down, tumbling and sliding, to the rocky floor of the shallow crater.

the voice came from within it—from within the crater. it could not be! he told himself that more than once. the rock of ganymede itself might carry sound, but you'd feel it only as a throbbing through the soles of your boots, for the vacuum of space which encroached on all sides could not transmit sound-waves.

that was science. that was elementary. but the voice whispered in his ears, ebbing and flowing, first loud, then soft—and science be damned.

charlie was calling. i am charlie stedman. i am charlie stedman—that was all, but it was enough. charlie's name, and charlie's voice.

"it can't be happening," steve said, aloud, and heard his own voice roaring inside the helmet. it drove the other voice, the impossible voice, out for a moment, but it returned. around the inner circumference of the ringwall steve ran, seeking a source for the impossible. sobbing, stumbling, he plunged ahead. it was only when he returned to his starting point, a needle-like pinnacle of rock, that he realized his supply of air would be exhausted in three hours.