Hex And The City by Simon R. Green

A streetwise private investigator who can see the supernatural works in the Nightside, a hidden, pitch-black London where monsters, magicians and dangerous bargains thrive; when a new case drags him into the city’s most corrupt and magical corners he must use wit, grit and moral flexibility to confront ancient powers, lethal creatures and human treachery in order to survive and unravel the truth.

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