Little Eve by Catriona Ward

On the wind-battered isle of Altnaharra, off the wildest coast of Scotland, a clan prepares to bring about the end of the world and its imminent rebirth.

The Adder is coming and one of their number will inherit its powers. They all want the honor, but young Eve is willing to do anything for the distinction.

A reckoning beyond Eve’s imagination begins when Chief Inspector Black arrives to investigate a brutal murder and their sacred ceremony goes terribly wrong.

And soon all the secrets of Altnaharra will be uncovered.