Scott knew what had happened. There was no need to guess. Only one thing could have happened. The liquid oxygen had united with the gasoline, making an explosive that was sheer death itself. A single tremor, a thrown stone, a vibration ... anything would set it off. Across the space between himself and the ship came the tattered figure of a man. A man whose clothes were torn. A man covered with blood, weaving, head down, feet dragging. "Jimmy!" yelled Scott. He sprinted forward but before he could reach his side, Jimmy had collapsed. Kneeling beside him, Scott lifted the man's head. The eyes rolled open and the lips twitched. Slow, tortured words oozed out. "I'm sorry ... Scott. I don't know why...." The eyes closed but opened again, a faint flutter, and more words bubbled from the bloody lips. "_I wonder why I did it!_" Scott looked up and saw his brother standing in front of him. Hugh nodded. "The Martians again, Scott. They could use Jimmy's mind. They could get hold of him. That blasted brain of his...." Scott looked down at the man in his arms. The head had fallen back, the eyes were staring, blood was dripping on the sand. "Hugh," he whispered, "Jimmy's dead." Hugh stared across the sand at the little glimmer of white in the shadow of the building. "We'll make another cross," he said. IV The Martians hadn't wanted them to to come. That much, at least, was clear. But having gotten here, the Martians had no intention of letting them return to Earth again. They didn't want them to carry back the word that it was possible to navigate across space to the outer planet. Maybe the Martians were committed to a policy of isolation. Maybe there was a "Hands Off" sign set up on Mars. Maybe a "No trespassing" sign. But if that had been the case, why had the Martians answered the radio calls from Earth? Why had they co-operated with Dr. Alexander in working out the code that made communication possible? And why did they continue sending messages and rockets to the Earth? Why didn't they sever diplomatic relationship entirely, retire into their isolation? If they didn't want Earthmen to come to Mars why hadn't they trained guns on the two ships as they came down to the scarlet sand, wiped them out without compunction? Why did they resort to the expedient of forcing Earthmen to bring about their own destruction? And why, now that Harry Decker and Jimmy Baldwin were dead, didn't the Martians wipe out the remaining two of the unwanted race? Perhaps the Martians were merely efficient, not vindictive. Maybe they realized that the remaining two Earthmen constituted no menace? And maybe, on the other hand, the Martians had no weapons. Perhaps they never had held a need for weapons. It might be they had never had to fight for self preservation. And above and beyond all ... what and where were the Martians? In that huge building? Invisible? In caverns beneath the surface? At some point far away?