Jennifer Morgue

Bob Howard is an IT expert and occasional field agent for the Laundry, the branch of Her Majesty's Secret Service that deals with occult threats.

Dressed (grudgingly) in a tux and sent to the Caribbean, he must infiltrate a millionaire's yacht in order to prevent him from violating a treaty that will bring down the wrath of an ancient underwater race upon humanity's head. Partnered with a gorgeous American agent who's actually a soul-sucking succubus from another dimension, Bob's mission (should he choose to accept it) is to stop the bad guys, avoid getting the girl, and survive - shaken, perhaps, but not stirred.

Book 2 in the Laundry Files series.