Sub-sea world of Venus. Allen saw little of it then, but still enough to suggest its ramified weirdness. They sped out through the watery tunnel, down the inlet at a depth of perhaps fifty feet, and then into the open sea. Empty, black-green depths. Running at fifty feet submersion, Allen could see beneath them the vague vista of a slimy undulating bottom. Then it dropped away, with only occasional jagged spires of peaks. Tumbled, submarine world. Fishes flipped away, frightened by the light. Occasionally, there was a glimpse of monstrous things that quivered; shapes that hung suspended, watching with dull-green round eyes. A submarine forest for a time was to one side, an intricate tracery of vegetation, with air-pods holding it upright as it slowly weaved and undulated like a thing quivering with life. A gigantic thing like a great squid with weaving tentacles came wobbling from a forest glade. It lunged to attack, but the little cylinder avoided it and sped past. Leh hardly spoke. He was tense, guiding their frail craft; and tense too with this emergency of haste to get to Peters. Leh had learned as much or more of Tollgamo's plans than had Allen. Then at last they were nearing their destination. Allen had learned now that Peters and his men of science were not located in the city of Arron. They had laboratories, workshops and arsenal on a rocky island fortress. It was some twenty miles by water from Arron; within a mile or so of a partly submerged section of the forest, where a village known as the Water City was built. Allen saw the watery foundations of the Water City as the cylinder sped past. Then Leh was slackening, to land at a sub-sea dock beneath the arsenal. The dock's weird dark outlines presently were beside them. With air-renewer mechanisms like a pack on their shoulders, and a round transparent glassite helmet, which had an elastic gasket tightly fitting their throats, they emerged through the cylinder's little pressure lock into the water. Heavy shoes made them able to walk, with a pushing swaying shove. Leh, with a metal-tipped finger, touched a tiny metal plate on Allen's helmet. And Leh's voice, dim, muffled, sounded in Allen's ears. "You follow me. There will be a guard where we emerge." Allen swayed along a rocky path which was slowly ascending. The turgid, black-green depths here were dimly lighted by a glow from some unseen source. It was a tumbled, honeycombed submarine slope. Clumps of vegetation stood like black thickets to the sides. Ahead, the glow seemed brighter. Then suddenly Leh stopped his advance; stood rigid. Within the round, wholly transparent ball of his helmet his youthful face was tense. And his voice murmured. "Allen, look there!" They had no more warning than that. From a clump of tawny submarine vegetation nearby, two human figures suddenly emerged! Figures that stood as though startled for a second, and then came plunging to attack! V