Years after the appearance in the solar system of the immense, deserted spaceship named by its discoverers Rama, a second craft arrived, destined to become home for a group of human colonists. But now the colony has become a brutal dictatorship, committing genocide against its peaceful alien neighbours and terrorizing its own inhabitants.

Nicole Wakefield, condemned to death for treason, has escaped and crossed the Cylindrical Sea to the island of mysterious skyscrapers which the humans call New York. There she is reunited with her husband, and soon they are joined by others of their family and friends. But pursuit is not far behind and they are forced to flee to the subterranean corridors of New York inhabited by the menancing octospiders.