The colonists from Earth have spent a century in cold sleep to make the first journey, one way, to settle a planet in another solar system. Avalon seems perfect, a verdant, livable world still in its prehistoric age. The biologists and engineers who busy themselves planting and building scoff at the warnings of professional soldier Cadmann Weyland until a large, unnaturally fast and cunning predator begins stalking the colony. Learning how to kill the beast is only the first step, for they must then reevaluate their entire understanding of Avalon's ecology.