Earth is generations dead and humans have colonised Jupiter in massive orbiting rings. When a man goes missing at a rail station, an investigator follows the trail to a college town and the home of an ex-lover who studies old Earth science as part of a long-term project to restore life there. The missing person case leads to a remote corner of the colony and to a plot that could have devastating consequnces.

Great world-building, great characters, great mystery, excellent reader.