The sound had seemed to come from somewhere overhead. From the empty void above, where there was nothing at all until the cloud canopy was reached many thousands of feet up. One of the _Viking's_ crew bared his teeth in a sudden panic and lifted his ray-gun to fire blindly upward. Before he could pull the trigger there was a blinding blue flash and a crash like summer thunder. Captive lightning! The ray-gun flew from the man's hands and landed a few feet away, its wooden stock badly charred and its barrel a glowing mass of fused metal. "Let your weapons rest, for they are useless here!" commanded that same booming voice from above. "Whence came ye, strangers in odd clothing who have traveled in a ship like a blue whale? What do ye seek here in the Outer Isles?" Gerry stepped forward, a few feet ahead of the group. He shouted that they were a scientific exploring party who had come from Earth in a space-ship. There was a brief period of silence, as though men consulted in whispers. Then the voice called him again. "You there--the leader! The Council of Elders will talk with you. Go fifty paces to your right, to where there are two white stones, and then come forward between them. Do not be afraid. You will not be harmed." "Are you going to take the chance, Chief?" Steve whispered. Gerry nodded. "I'll have to." About fifty yards to his right Gerry saw two white stones. They were set some twelve or fifteen feet apart, on the very edge of the invisible barrier. Gerry walked over, turned left, and then walked squarely in between the stones. He held one arm protectingly in front of him, but this time his hand did not encounter any barrier. Instead--he found himself standing under the arch-way of a gate with a mighty city spread before him! * * * * * The city had simply appeared in a flash, with its mighty towers soaring up to the sky, as soon as he stepped over the outer line of the arch. Whatever it was that held the place invisible from outside, it had ceased to function for him as soon as he came within the limits of the outer surface of the walls. Glancing back, he saw that his companions were still staring blankly at the spot he had just quitted. They were evidently unable to see either him or any part of the city. "It's all right, Steve!" he shouted. "Just hold everybody there till I come back." Doors of heavily carved glass slid noiselessly out of recesses within the wall to close the gate through which Gerry had just entered. The arch in which he stood was inside the thickness of the wall, faced with white marble, inlaid with designs in gold. Ahead, he could see a broad avenue that ran from the gateway down through the center of the city. It was tree lined and pleasant, thronged with people. Flowers grew in little plots in front of the gold and white houses. Small furry animals, dogs, were evidently kept as pets. They drowsed on the doorsteps or scampered about the neat gardens.