The King of Dreams — Robert Silverberg

In the seventh and final volume in The Majipoor Cycle, Coronal Lord Prestimion has finally restored peace to Majipoor after years of unrest, but as he prepares for his ascension to the throne of Pontifex, the kingdom comes under attack by the scheming Mandralisca, who have unleashed a plague of madness on Majipoor's citizenry. Reprint.