Knox and Harper's story continues as the Las Vegas lair - and its two infamous Co-Primes - face their most terrifying enemy yet....

Together, Harper and Knox have overcome just about every evil thing you can think of - from Horsemen of the Apocalypse to dark magic practitioners to Lucifer's insistent belief that he's hilarious. They're looking forward to some well-earned downtime - until Harper is attacked by mercenaries in the middle of her tattoo shop. Worse still, the attackers are trying to take her wings - the ones no one is meant to know she even has.

It's a near miss, and once a furious Knox has managed to pull his demon back into line there's only one thing clear - someone knows Harper's secrets and is systematically setting out to destroy her. It seems likely that someone is the third Horseman - but how do they know so much about Harper? It seems the impossible might be true - they have an enemy hiding at the very heart of the lair.

To survive Harper will need to embrace power that's darker than she's ever experienced, and even Knox can't protect her from everything - though God knows nothing's going to stop him trying. The stakes have never been higher, for if Harper's taken by this new threat, Knox won't be able to stop his demon from taking a vicious pleasure in tearing the world apart....