From the back cover:
"From the depths of antiquity, he arises....
Trapped in a mockery of his former kingdom, he broods....
In hatred and spite against the one who betrayed him, he schemes....
The other lords of Ravenloft may possess horrific power...
but Vecna is a god.
Trapped by the Mists of Ravenloft, the lich lord Vecna plots his escape and revenge against Kas the Destroyer, his traitorous former lieutenant.
Vecna Reborn takes brave heroes into the dark, oppressed domain of Tor Gorak, where Kas whips his subjects into submission to serve in his never-ending war against Vecna and Cavitius, a realm in the grip of ancient magic and malevolent undeath. The heroes must struggle to stop arcane rituals, insane cultists, and monstrous abominations from granting Vecna, the Chained God, the power to fulfill his dark dreams. Vecna Reborn presents a terrifying tale of betrayal, madness, and sorcery that may tear apart the Demiplane of Dread itself."