He sat on a beach of pale grey sand. At his feet were the shallows of a grey-green lake that filled a stony basin some half-mile in breadth. To his left the underground river poured out of the cliff face, spreading into a wide, riffling fan of foam. Off to his right, the water spilled over the rim of the basin to become a river again somewhere below, and beyond the rim, veiled in mist and the shadow of a mountain wall, was a valley. Behind him, crowding to the edge of the sand, were trees and ferns and flowers, alien in shape and color but triumphantly alive. And from what he could see of it, the broad valley was green and riotous with growth. The water was pure, the air had a good smell, and it came to Trevor that he had made it. He was going to live a while longer, after all. Forgetting his weariness, he sprang up, and the thing that had hissed and screamed above him swooped down and passed the clawed tip of a leathery wing so close to his face that it nearly gashed him. He stumbled backward, crying out, and the creature rose in a soaring spiral and swooped again. Trevor saw a sort of flying lizard, jet black except for a saffron belly. He raised his arms to ward it off, but it did not attack him, and as it swept by he saw something that woke in him amazement, greed, and a peculiarly unpleasant chill of fear. Around its neck the lizard-thing wore a golden collar. And set into the scaly flesh of its head--into the bone itself, it seemed--was a sun-stone. There was no mistaking that small vicious flash of radiance. Trevor had dreamed of sun-stones too long to be misled. He watched the creature rise again into the steamy sky and shivered, wondering who, or what, had set that priceless thing into the skull of a flying lizard--and why. It was the _why_ that bothered him the most. Sun-stones are not mere adornments for wealthy ladies. They are rare, radioactive crystals, having a half-life one third greater than radium, and are used exclusively in the construction of delicate electronic devices dealing with frequencies above the first octave. Most of that relatively unexplored super-spectrum was still a mystery. And the strangely jewelled and collared creature circling above him filled Trevor with a vast unease. It was not hunting. It did not wish to kill him. But it made no move to go away. From far down the valley, muted by distance to a solemn bell note that rolled between the cliffs, Trevor heard the booming of a great song. A sudden desire for concealment sent him in among the trees. He worked his way along the shore of the lake. Looking up through the branches he saw the black wings lift and turn, following him. The lizard was watching him with its bright, sharp eyes. It noted the path of his movements through the ferns and flowers, as a hawk watches a rabbit.