In the 24th century, humanity has colonized the solar system. The UN has risen to become a world government, and Mars is an independent military power. Both planets depend on the scarce resources of the asteroid belt, which are mined there under harsh conditions by the Belters. A militant resistance group, the Outer Planets Alliance (OPA), has formed among them. The solar system teeters on the brink of war; a single spark could ignite it...