From back cover:

"Created in an ancient war, implacable machines programmed to destroy all life, they seem invincible. But now humanity has come to a berserker base: Lars, a prisoner of war who will not surrender; the crew of Aster's Hope, peaceful explorers who must now learn to fight; and Holt and Morgan, who will use the alien skills of the primitive 'Reen to face the planet killers."