The heavy grass, standing waist-high in the little valley where their ship was at rest, stirred to ripples of vivid green as a light breeze touched it. Above, the sun shone warm upon this world of tropical growth. Harkness, listening in the utter silence for sounds that might mean danger, let his eyes follow up the rugged wall of rock that hemmed them in on two sides. It gleamed with metallic hues in the midday glare. He looked on to the sun above. "A dark moon!" he said wonderingly. "Dark!--and yet it is blazing bright. Why can't we see it from Earth? Why is it dark?... I've an idea that the gas we came through is the answer. There is metal, we know, that conducts an electric current in only one direction: why not a gas that will do the same with light?" * * * * * The pilot was listening, but Diane seemed uninterested in scientific speculations. "The trees!" she breathed in rapture; "the marvelous, beautiful trees!" She was gazing toward distant towering growths where the valley widened. Like no trees of Earth, these monsters towered high in air, their black trunks branching to end in tendrils that raised high above them. And the tendrils were a waving, ever-moving sea of color, where rainbow iridescence was stabbed through with the flash of crimson buds. A down-draft of air brought a heady, intoxicating odor. And still there was silence. To Walter Harkness, standing motionless and alert amidst the waving grass, it seemed a hush of waiting. A prickle of apprehension passed over his skin. He glanced about, his pistol ready in his hand, looked back for a moment at the ship, then smiled inwardly in self-derision of his fear as he strode forward. "Let's have a look at things," he said with a heartiness not entirely sincere. "We'll discover nothing standing here." But the silence weighed upon them all as they pressed on. No exclamations of amazement from them now, no speculations of what might lie ahead. Only wide-eyed alertness and a constant listening, listening--until the silence was broken by a scream. A man it seemed at first, when Harkness saw the figure leap outward from the cliff. A second one followed. They landed on all fours upon a rock that jutted outward toward the trees. The impact would have killed a human, but these creatures stood upright to face the concealment from which they had sprung. One was covered with matted, brown hair. Its arms were long, and its fists pounded upon a barrel-like chest, while it growled hoarsely. The other ape-thing, naked and hairless, did the same. They were both uttering those sounds, that at times seemed almost like grunted words, when the end came. A swishing of leather wings!--a swooping, darting rush of a huge body!--and one of the ape-men, as Harkness had mentally termed them, was struggling in the clutch of talons that gripped him fast.