What had made an invulnerable Krak wince at the blows from an Earthman's fist? * * * * * There were no earthly words to describe Karrar, the home planet of the Kraks. Karrar was Karrar--a stupendous planet, brooded over by a sullen sun, a land of harsh reds and blacks. Impassive it was--as indestructible as its spawn of Kraks. They'd known when the landing had been made, for the Kraks, their blank faces rigid, had come into the prison room and roughly strapped a metal contrivance on the back of each Earth person, man, woman and child. For such a sullen-looking planet, Sean decided, the weather was exceedingly cold, striking at his flesh and bones like tiny needles. The Kraks herded the long line of humans through the airlock out onto the huge expanse of the space port. There were thousands of ship cradles, it seemed, and they were packed with other ships unloading their cargo. As far as his green eyes could see, Sean recognized only human beings--thousands of them moving single file out of the maws of the swollen Krak ships. Those files were converging at a huge gate at the far end of the port. They looked, Sean thought, like long lines of ants moving toward their hill. Then he, too, was moving toward the same gate. Perhaps only he, of those thousands, was different. For he was not squeezed into the line. The human ahead of him and the human behind were a good four feet from him, as if keeping as far from a carrier of the plague as possible. Sean grinned wryly. He kept his eyes fixed ahead where black buildings shoved their coarse heavy structures against the lowering scarlet sky. They moved through the mammoth portal at last, and finally Sean was swept into the mass of humans who clogged the way. They stumbled through the black block-paved streets and the few Kraks who were on the street gave those humans only cursory glances. Nothing new to them, Sean thought grimly. And the urgency of his conviction that these Kraks could be destroyed put buoyancy in his step and set his mind to working frantically. He towered above the other humans around him, his flame-hair blazing like a torch. A Krak saw that flame head. Sean didn't know it then, but he learned shortly. Finally those thousands of humans were herded into an open-air compound, surrounded by heavy, black stone walls that lifted breathtakingly above them. Other humans were there, men bearded and filthy, women, even in their despair, trying to keep some semblance of beauty. The clothes of these older prisoners were almost gone, only that metal contrivance on their backs shone brightly. Many of the children, even in the cold of Karrar, moved about listlessly, naked. Sean counted seven fist and kick fights going on in the compound as he entered.