The Regicide Report

An occult assassin, an elderly royal and a living god face off in The Regicide Report, the thrilling final novel in Charles Stross' epic, Hugo Award-winning Laundry Files series. When the Elder God recently installed as Prime Minister identifies the monarchy as a threat to his growing power, Bob Howard and Mo O'Brien - recently of the supernatural espionage service known as the Laundry Files - are reluctantly pressed into service. Fighting vampirism, scheming American agents and their own better instincts, Bob and Mo will join their allies for the very last time.

God save the Queen- because someone has to.