After regaining her memories and saving the reptilian Hsktskt from a devastating plague, Dr. Cherijo Torin faces a different kind of epidemic--a mysterious black crystal spreading like cancer throughout the galaxy. A mercenary claiming to have information on the crystal's origins leads Cherijo and her husband Duncan Reever to the planet Trellus, and maroons them there.   Trellus is a world under quarantine. Its colonists exhibit excessive paranoia and anger, taking out their frustrations in the Omega Dome in simulated combat against battle drones. But someone--or something--is killing victims outside the arena, leaving only their skins behind. Cherijo believes the black crystal infection is responsible for this horror--and that someone deliberately triggered the outbreak.