Brother Assassin - Fred Saberhagen

On the planet Sirgol the death machines have a unique and sublte mode of attack. Now, the time and place of the next attack has been pinpointed--the berserkers will try to eliminate Vincent Vincento, an early genius whose loss will cost mankind a hundred years of progress in the physical sciences. Derron Odegard, one of the elite corps of Time Operatives, has the toughest assignment in Sirgol's history--protect Vincento at any cost.