Mate Magic by S. King

Supernatural P.I. Aster Night is closing in on a killer, but soon finds herself caught in the cross fire of some pitch black magic.
Demon magic.
The only way to save herself–and the world–is to catch the killer before he strikes again.
She’s going to need every bit of magical help she can get…including the assistance of her three drop-dead sexy new boyfriends. Together, she, Rake, Damon, and Finn are a force to be reckoned with. Every time they touch, power and passion flare in equal measure.
The power, she needs.
The passion, is a distraction she can’t afford.
But when the ultimate darkness threatens the four fated mates, love may be the only magic strong enough to save them.