Mortal Magic: dark urban fantasy

It will take a mortal soul to claim an immortal magic.
Brie is willing to do what it takes in order to destroy the Cult of Blackburn before it can harm one more witch, even if it means striking a pact with a most unlikely ally. But then she discovers the pact comes with a trip to Hell. As the search for her mother's bones turns deadly, she realizes she's made a mistake. A grave one. Because raising a necromancer from the dead takes the blood of a god. A lot of blood. And there's no way to ac...