Freshly graduated and commissioned, Space Marine Lt. Carrie Piper, already contending with inter-service rivalry with the Navy crewmen with whom she serves, is tasked with retrieving an asteroid made of pure thorium from the asteroid belt and bringing it to Earth for use as fissionable material. She is opposed by agents of the Confederation of Peoples Governments, who will do anything, even risk starting an interstellar war, to seize control and take possession of the asteroid.