Season of skulls / Charles Stross.

Sequel to: Quantum of nightmares.

Hyperorganized and formidable, Eve Starkey defeated her boss, the louche magical adept and billionaire Rupert de Montfort Bigge, in a supernatural duel to the death. At least, she has reason to hope he's dead. But though she's now in charge of the Bigge Corporation, she's not free of him yet. Through the fecklessness of her brother Imp, combined with the intricate feudal law of a tiny Channel Island, it would appear that unbeknownst to her, she was married to Bigge and that proving his death and releasing herself from his arcane bindings will take years and cost millions. Then an emissary of the Prime Minister arrives with an offer that she absolutely can't well, you know.