Spook's, Slither's Tale

Far from the Wardstone, a new darkness is rising . . .
Slither is a haizda mage who preys upon humans, drinking their blood to feed his dark urges. So when a local farmer dies, it's only natural that Slither should want to feast on his lovely daughters.
But then the farmer offers him a deal, and extracts from Slither a promise that will take him on a journey to the City of the Petrified Tree, to a fallen star-stone that holds great power, and straight into the path of Grimalkin, the Witch Assassin.
The series that inspired the forthcoming movie The Seventh Son, starring Jeff Bridges, Ben Barnes and Julianne Moore.