"If they want us," answered Jill, deliberately missing the point. "Do you think you have the right to destroy all we've worked for?" Gray was silent. Rather grimly, she went on. "Caron of Mars would like to see us defeated. He didn't care about Mercury before radium was discovered. But now he'd like to turn it into a prison mining community, with convict labor, leasing mine grants to corporations and cleaning up big fortunes for himself and his associates. "Any trouble here will give him an excuse to say that we've failed, that the Project is a menace to the Solar System. If you try to escape, you wreck everything we've done. If you don't tell the truth, you may cost thousands of men their futures. "Do you understand? Will you cooperate?" Gray said evenly, "I'm my own keeper, now. My brother will have to take care of himself." It was ridiculously easy, she was so earnest, so close to him. He had a brief kaleidoscope of impressions--Ward's sullen bewilderment, Moulton's angry roar, Dio's jerky rise to his feet as the guards grabbed for their guns. Then he had his hands around her slim, firm throat, her body pressed close to his, serving as a shield against bullets. "Don't be rash," he told them all quietly. "I can break her neck quite easily, if I have to. Ward, unlock that door." In utter silence, Ward darted over and began to spin the dial. At last he said, "Okay, c'mon." Gray realized that he was sweating. Jill was like warm, rigid marble in his hands. And he had another idea. "I'm going to take the girl as a hostage," he announced. "If I get safely away, she'll be turned loose, her health and virtue still intact. Good night." The clang of the heavy door had a comforting sound behind them. * * * * * The ship was a commercial job, fairly slow but sturdy. Gray strapped Jill Moulton into one of the bucket seats in the control room and then checked the fuel and air gauges. The tanks were full. "What about you?" he said to Ward. "You can't go back." "Nah. I'll have to go with you. Warm her up, Duke, while I open the dome." He darted out. Gray set the atmosphere motors idling. The dome slid open, showing the flicker of the auroras, where areas of intense heat and cold set up atmospheric tension by rapid fluctuation of adjoining air masses. Mercury, cutting the vast magnetic field of the Sun in an eccentric orbit, tortured by the daily change from blistering heat to freezing cold in the thin atmosphere, was a powerful generator of electricity. Ward didn't come back. Swearing under his breath, tense for the sound of pursuit in spite of the girl, Gray went to look. Out beyond the hangar, he saw a figure running. Running hard up into the narrowing cleft of the valley, where natural galleries in the rock of Mercury led to the places where the copper cables were anchored, and farther, into the unexplored mystery of the caves.