The book begins with a prologue recording a mutiny aboard the planetoid-sized "Utu"-class starship of the Fourth Imperium (a more-than-55,000-year-old technologically advanced multi-star system empire), the "Dahak", led by its Chief of Engineering, the ambitious and psychopathic Captain Anu and Commander Inanna. Anu's reason for mutiny is to lead his followers to refuge on a planet where presumably the genocidal wrath of the "Achuultani", a mysterious alien race that periodically exterminates all intelligent life it can find, which has also destroyed the previous three Imperiums and the dinosaurs, will pass over them.