City of Torment — Bruce R. Cordell

Raidon Kane travels to the subterranean fortress of the somnambulant aboleths, bent on killing the Eldest in its sleep. But he isn't the only one bound for the hidden city. A warlock, an arch fey, a pirate, and a high priestess of the Abolethic Sovereignty all have designs of their own on the Eldest -- if they don't kill each other first.