Elminster In Hell by Ed Greenwood

Dragged into the infernal layers of the Nine Hells, the aging and cunning sage Elminster endures relentless torment and manipulation as devils and demons try to break him and exploit his knowledge; stripped of much of his power and forced to confront the consequences of a long, complicated life, he revisits memories, forges uneasy alliances with fellow captives and unexpected allies, and relies on wit, hidden magics, and stubborn defiance to resist infernal bargains and mount a desperate struggle for escape and retribution that echoes back into the mortal world.

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