They were gigantic--three times the size of any he'd ever seen before. Within the corolla lay half-a-dozen concentric rings of thread-like, sharply differentiated tendrils. He frowned; spoke half to himself: "Which are the stamens?" "Or are there any?" Eileen slid a fingernail across the rippling tendrils. "Maybe this is a different kind of plant than we know--one based on six sexes instead of two." "Maybe." Still frowning, Boone picked another flower to study. Again, as earlier up in the carrier-cradle, he was acutely conscious of the blackness pressing in about them; the utter silence. It brought a queer prickling along his spine. Eileen brushed against him. "Fred, why can't we let this wait till morning? After all, what do we know about this place, or the Helgae?" There was a tremor in her voice. "The Helgae?" Stubbornly, Boone shrugged off his own mood. "If they could do anything to humans, they'd have done it when IC started operations out on Titan. As for this place--" He tilted the light-rod up to illuminate the ground ahead. Its beam stopped short a bare six feet before them, cut off as completely as by a wall. Eileen clutched his arm. "Fred--!" Boone whipped the beam left. Six feet it carried; no more. Whirling, he pointed it back in the direction from which they had come, squarely at the sphere-ship. But there was no ship; or if there was, the light-beam could not reach it. Panic gripped Boone--the black, surging panic that roars up in a tidal wave when Man stands face to face with the unknown. Dimly, he knew that Eileen had swayed against him; that instinctively he'd thrown his arm about her. That was all. Yet in spite of it, now, he forced himself into striding forward--one creaking step ... two ... three.... The light-beam shortened with each step. The truth dawned on him, then: The beam stopped short as if cut off by a wall ... because, indeed, a wall had risen up before it! A dull, translucent wall of silvery grey. Numbly, he lanced the beam skyward. There, too, it broke on the grey shell. Boone's panic channeled into fury. He spun about; struck savagely at the barrier. Blood spurted from split knuckles. The wall remained. Twisting, he hurled his full weight against the barrier. Again, it threw him back. He straightened, then; swung round the light-rod, searching the shell for some flaw, some weakness. He found none. Beside him, Eileen was sobbing. "Fred, what's happened?" "What's happened--?" Boone laughed, a harsh and bitter laugh. "We're trapped, Eileen; that's what: Trapped in a Helgae bubble like those domes we saw!" Her tears died. She stared at him. "But the Helgae can't hurt humans--" "They can't?" He threw out the query like a challenge. "What do we really know about it?" "But--on Titan--"