Sean Connery stars as Federal District Marshal William T. O'Niel, assigned to a mining outpost on the Jovian moon Io. The highly productive titanium mine seems to be the backwater of the universe, but the miners are killing each other in strangely psychotic ways. Now, hired assassins are trying to kill O'Niel to bury the secret his investigation has revealed ... and there's no one he can call for help in this far end of the solar system.