The weapon he had chosen was simplicity itself—a hand-sized capsule of oxygen. But in a hydrogen/ammonia atmosphere, oxygen could be a deadly explosive. Massan carried several of these “bombs”; so did Odal. _But the trick_, Massan thought to himself, _is to know how to throw them under these conditions; the proper range, the proper trajectory. Not an easy thing to learn, without years of experience._ The terms of the duel were simple: Massan and Odal were situated on a rough-topped iceberg that was being swirled along one of the methane/ammonia ocean’s vicious currents. The ice was rapidly crumbling; the duel would end when the iceberg was completely broken up. Massan edged along the ragged terrain. His suit’s grippers and rollers automatically adjusted to the roughness of the topography. He concentrated his attention on the infrared detector that hung before his viewplate. A chunk of ice the size of a man’s head sailed through the murky atmosphere in a steep glide peculiar to heavy gravity and banged into the shoulder of Massan’s suit. The force was enough to rock him slightly off-balance before the servos readjusted. Massan withdrew his arm from the sleeve and felt the inside of the shoulder seam. _Dented, but not penetrated._ A leak would have been disastrous, possibly fatal. Then he remembered: _Of course—I cannot be killed except by direct action of my antagonist. That is one of the rules of the game._ Still, he carefully fingered the dented shoulder to make certain it was not leaking. The dueling machine and its rules seemed so very remote and unsubstantial, compared to this freezing, howling inferno. He diligently set about combing the iceberg, determined to find Odal and kill him before their floating island disintegrated. He thoroughly explored every projection, every crevice, every slope, working his way slowly from one end of the ’berg toward the other. Back and forth, cross and re-cross, with the infrared sensors scanning three hundred sixty-degrees around him. It was time-consuming. Even with the suit’s servomotors and propulsion units, motion across the ice, against the buffeting wind, was a cumbersome business. But Massan continued to work his way across the iceberg, fighting down a gnawing, growing fear that Odal was not there at all. And then he caught just the barest flicker of a shadow on his detector. Something, or someone, had darted behind a jutting rise of the ice, off by the edge of the iceberg. * * * * * Slowly and carefully, Massan made his way toward the base of the rise. He picked one of the oxy-bombs from his belt and held it in his right-hand claw. Massan edged around the base of the ice cliff, and stood on a narrow ledge between the cliff and the churning sea. He saw no one. He extended the detector’s range to maximum, and worked the scanners up the sheer face of the cliff toward the top.