Peak of the Devil - The Adventures of Lydia Trinket, #2

Lydia Trinket thought she was free of the netherworld and the ghosts she left behind. Turns out she was only half right. Now those ghosts are back in the real world, with new plans, new powers, and old grudges. When it becomes clear that possessing teenage girls and stealing human hearts is only the beginning, it falls to Lydia to hunt down the malevolent spirits and banish them for good. Preferably before anyone else gets killed.
A task she would almost certainly be up to, if one of them hadn't made a deal with the devil.