"Suppose," I said, "that you had a little compartment inside a pipe of flowing gas or liquid. That's what Maxwell said. Suppose the compartment had a little door that allowed molecules to enter or leave. You station a demon--that's what Maxie called them himself--at the door. The demon sees a hot molecule coming, he opens the door. He sees a cold one, he closes it. By and by, just like that, all the hot molecules are on one side of the door, all the cold ones--the slow ones, that is--on the other. Steam on one side, ice on the other, that's what it comes down to." "That was what you saw with your own eyes," Theobald Greco reminded me. "I admit it," I said. "And I admit I didn't understand. But I do now." I understood plenty. Separate isotopes--separate elements, for that matter. Let your demon open the door to platinum, close it to lead. He could make you rich in no time. He had, in fact, done just that for Greco. * * * * * Greco said, "Here. First installment." He pulled something out of his pocket and handed it to me. It was metallic--about the size of a penny slot-machine bar of chocolate, if you remember back that far. It gleamed and it glittered. And it was ruddy yellow in color. "What's that?" I asked. "Gold," he said. "Keep it, Virgie. It came out of sea water, like you said. Call it the down payment on your salary." I hefted it. I bit it. I said, "By the way, speaking of salary...." "Whatever you like," he said wearily. "A million dollars a year? Why not?" "Why not?" I echoed, a little dazed. And then I just sat there listening, while he talked. What else was there to do? I won't even say that I was listening, at least not with the very fullest of attention, because that thought of a million dollars a year kept coming between me and his words. But I got the picture. The possibilities were endless. And how well I knew it! Gold from the sea, sure. But energy--free energy--it was there for the taking. From the molecules of the air, for instance. Refrigerators could be cooled, boilers could get up steam, homes could be heated, forges could be fired--and all without fuel. Planes could fly through the air without a drop of gasoline in their tanks. Anything. A million dollars a year.... And it was only the beginning. I came to. "What?" He was looking at me. He repeated patiently, "The police are looking for me." I stared. "_You?_" "Did you hear about Grand Rapids?" I thought. "Oh--Wait. A fire. A big one. And that was you?" "Not me. My demons. Maxwell demons--or Greco demons, they should be called. He talked about them; I use them. When they're not using me. This time, they burned down half the city." "I remember now," I said. The papers had been full of it. "They got loose," he said grimly. "But that's not the worst. You'll have to earn your million a year, Virgie." "What do you mean, they got loose?" He shrugged. "Controls aren't perfect. Sometimes the demons escape. I can't help it."