I didn't smile. "And what would you have me do about it?" "Stop following me, of course, sir." "Very well," I said. "I won't follow you any more. Will that be satisfactory?" "Quite, sir." Without another word, he picked up his butterfly net and disappeared along a path that led through a rock crevice. Only then did I allow myself to grin. It was a sad and pitying and affectionate kind of grin. I sat down and did with my shoes as he had done. There wasn't any hurry; I knew where he was going. There could only be one place, of course--the city of Deimos and Phobos. Other than that he had no choice. And I thought I knew the reason for his going. Several times in the past, there have been men who, bitten with the fever of an idea that somewhere on this red planet there must be gold, have done prospecting among the ruins of the old temples. He had probably heard that there were men there now, and he was carrying out with the thoroughness of his precise little mind the job he had set himself of finding the killer of his daddy. I took a short-cut over the rag-cliffs and went down a winding, sand-worn path. The temple stones stood out barren and dry-looking, like breast bones from the desiccated carcass of an animal. For a moment I stopped and stared down at the ruins. I didn't see the boy. He was somewhere down there, though, still swinging his butterfly net and, probably, still whistling. I started up once more. And then I heard it--a shrill blast of sound in an octave of urgency; a whistle, sure, but a warning one. I stopped in my tracks from the shock of it. Yes, I knew from whom it had come, all right. But I didn't know why. And then the whistle broke off short. One instant it was in the air, shrieking with a message. The next it was gone. But it left tailings, like the echo of a death cry slowly floating back over the dead body of the creature that uttered it. I dropped behind a fragment of the rag-cliff. A shot barked out angrily. Splinters of the rock crazed the morning air. The little boy screamed. Just once. I waited. There was a long silence after that. Then, finally, I took off my hat and threw it out into the valley. The gun roared once more. This time I placed it a little to the left below me. I took careful sighting on the hand that held that gun--and I didn't miss it. It was Harry Smythe, of course. When I reached him, he had the injured hand tucked tightly in the pit of his other arm. There was a grim look in his eyes and he nodded as I approached him. "Good shooting, mate. Should be a promotion in it for you. Shooting like that, I mean." "That's nice to think about," I said. "Where's the boy? I owe him a little something. If he hadn't whistled a warning, you could have picked me off neat." "I would." He nodded calmly. "Where is he?" "Behind the rock there. In that little alcove, sort of." He indicated with his chin. I started forward. I watched him, but I went toward the rock. "Just a minute, mate."