In the distant future humanity has taken to the stars and has begun to explore the galaxy. Numerous worlds are discovered and colonized. Among the recently discovered is Planet Theta Alpha Yankee Four, a world eerily similar to Earth. The United Earth has built an outpost, Outpost Sierra, to research the planet and its solar system. When a distress signal is received from Outpost Sierra, the Earth Defense Force Ship Centaur is dispatched to respond to the signal. Marine 2nd Lieutenant Michael Taylor and a team of clone Marines are sent to the surface to discover the nature of the station's emergency. Soon Taylor and his Marines are in a desperate fight for survival, and in the process they stumble across an ancient truth that could change them and the rest of humanity.