The Spy Who Haunted Me by Simon R. Green

Eddie Drood, at your service. For generations my family has been keeping humanity safe from the wicked, the nasty, and the generally not-nice inhuman predators who feed on people’s fear and misery. No one kicks evil arse better than us Droods—especially yours truly.

In fact, my arse-kicking skills have come to the attention of the legendary Alexander King, Independent Agent extraordinaire, who spent a lifetime doing anything and everything—for the right price. Now he’s on his deathbed, looking to bestow all of his priceless secrets to a worthy successor.

To decide, King challenges six competitors—myself included—to solve five mysteries all around the world, figuring that along the way we’ll backstab one another until only one remains. But I’ve got to win at all costs, because King holds the most important secret of all to the Droods: the identity of the traitor in our midst.