I lowered my arm. His outburst seemed faintly childish to me. And yet it carried a good measure of common sense. If we discovered proof of an alien race, we would indeed be famous. The more we discovered for ourselves, the more famous we'd be. Fame was practically a synonym for prestige and wealth. "All right," I conceded. Miller stepped forward, moving slowly in the bulk of his spacesuit. Deliberately, he removed a small torch from his side and pressed the brilliant flame against the metal. A few minutes later, the elderly mineralogist gave his opinion: "It's steel ... made thousands of years ago." Someone gasped over the intercom, "Thousands of years! But wouldn't it be in worse shape than this if it was that old?" Miller pointed at the small cut his torch had made in the metal. The notch was only a quarter of an inch deep. "I say _steel_ because it's _similar_ to steel. Actually, it's a much stronger alloy. Besides that, on the Moon, there's been no water or atmosphere to rust it. Not even a wind to disturb its surface. It's _at least_ several thousand years old." * * * * * We slowly circled the alien structure. Several minutes later, Kane shouted, "Look!" A few feet above the ground, the structure's smooth surface was broken by a circular opening that yawned invitingly. Kane ran ahead and flashed his head-lamp into the dark recess. "There's a small room inside," he told us, and climbed through the opening. We waited outside and focused our lamps through the five-foot opening to give him as much light as possible. "Come on in, Marie," he called to his wife. "This is really something! It _must_ be an alien race. There's all kinds of weird drawings on the walls and gadgets that look like controls for something...." Briefly, my lamp flickered over Marie's pale face. Her features struggled with two conflicting emotions: She was frightened by the alienness of the thing and yet she wanted to be with her husband. She hesitated momentarily, then climbed through the passage. "You want to go in?" my wife asked. "Do you?" "Let's." I helped Verana through the opening, climbed through myself and turned to help Miller. Miller was sixty years old. He was an excellent mineralogist, alert mentally, but with a body that was almost feeble. I reached out to help him as he stepped into the passageway. For a brief second, he was framed in the opening, a dark silhouette against the star-studded sky. The next second, he was thrown twenty yards into the air. He gasped with pain when he struck the ground. "_Something_ pushed me!" "Are you all right?" "Yes." He had fallen on a spot beyond our angle of vision. I started through the passage.... ... and struck an invisible solid wall. * * * * * My eyes were on the circular opening. A metal panel emerged from a recess on one side and slid across the passage. The room darkened with the absence of starlight. "_What happened?_"