It is about problems that the inhabitants of a huge generation space ship face after an alien amino acid that they picked up on another planet triggers a pandemic.

[2] The novel's protagonist, Roy Complain, lives in a culturally primitive tribe on a massive generation ship, which has descended into an uncivilized state.

After his wife is kidnapped, a tribal priest, Marapper, encourages Complain to join a furtive expedition into the unexplored corridors.

Marapper believes that they are all living on board a moving spacecraft and that if they can reach the control room, they will gain command of the entire gargantuan vessel.

In a previous generation, the ship's inhabitants had suffered from a pandemic because of an alien amino acid found in the waters of the Procyon planet.

Meanwhile, Complain and his developing romantic interest, Vyann, a Forward officer, learn that the spacecraft should have taken only six generations to return to Earth.

Aware that 23 generations have passed since the epidemic, they despairingly deduce that the entire spacecraft is now plummeting into the cold expanse of infinite space.

However, the recent battle on board the spacecraft has caused it to begin an emergency split into its composite parts, which ensures that the entire population will now be granted a new start on Earth.