This is the Fifteenth (#15) in an number of tie-in novels of Ravenloft Gothic horror tales dealing with the masters and monsters set in the Demiplane of Dread.
Once a powerful human wizard, Firan Zal'honan is transformed into Azalin, the King of the Dead, an anguished undead ruler with limitless dark powers, who can neither gain his own freedom nor bring back to life his long-dead son.