It has been 25 years since the ore spaceship Siberia was last heard from. Unfortunately, it is now on a collision course with the communications station Comstat 5 which is orbiting Mars. After one successful maneuver to avoid the Siberia, it rams Comstat 5 and the crew soon finds that the Siberia crew is dead and the reason that it has been missing for 25 years. But that reason is trying to destroy them all as it destroyed the Siberia crew.