A hundred yards beyond was a milky-white mistiness reaching from wall to jungle wall. And this was not Venusian fog! It remained quiescent. An unearthly blue radiance seemed to shine beyond, giving an impression of vast distance. Curt said brusquely, "Wait here. Keep out of sight!" He hurried forward, keeping to the tangled jungle wall wherever possible. As he neared the barrier, it tended toward a semi-translucence. The bluish light beyond seemed to have no source, and Curt had the impression of a vast grotto that reached interminably above, curving away into the fog. Now he could see vague outlines beyond, towering and bulky. Other shapes moved about, appearing to Curt as shadows seen through faintly frosted glass. "Buildings--and people!" Undoubtedly, the silver spacer had come here; there was probably an overhead entrance. Curt moved closer, and heard the faintest murmur of sound beyond, as of men and machines at work. Excitement caught at his brain. Now he knew, with sharp certainty, that he'd found the thing that DeHarries and other planetary leaders were seeking! Only for some inimical purpose would men, whoever they were, band together in so secret and inaccessible spot as K'Yarthan Swamp! Curt examined the barrier. It was some sort of power screen; he felt a dangerous radiation that decided him against trying his electro on it. He hurried back to the others. "Can't tell how far it extends," he told them. "It's an Electronic Curtain, that's for sure! And there are men and buildings behind it." "We've got to find an entrance somewhere." A terrible grimness took hold of Lorine, as she thought of her father. But Curt shook his head doubtfully. "If we tried our electros on it--" This came from Tor Ekkov, and Curt laughed mirthlessly. "Sure, you try that, if you're tired of your present identity. It would turn you into a billion disorganized electrons!" "I have an idea." Lorine turned back to the swamp edge. She stood pondering, staring at the stern of the alien spacer. "How far would you say that goes beneath the surface?" They saw her meaning, as she pointed out the angle of the stern. The spacer was gigantic, and the other end should almost certainly reach somewhere beneath the Electronic Curtain! They set to work at once. By strewing thick foliage across the mud they formed a path that bore their weight. With electros at pencil-thin sharpness, they began on the spacer hull. The metal was strange and tough, uncorrosive. Its atomic structure resisted. But after a long while it began to soften, then to melt away in radiant froth. A circular section gave way, fell slowly inward. Flash-beams revealed a long empty corridor sloping gently down.