Hidden Allies. The Living Oracle, #4

Helena Campbell, oracle and mother, has lost much thanks to the secret war between her allies, the magic-wielding Wardens, and their enemies the Savants. With friends disappearing or injured, her beloved home destroyed, and her children's lives at risk, she knows what threats to defend against. That is, until elves trapped for a thousand years of poisoned imprisonment join the fight, looking for revenge.
When a fugitive elf woman dies in her backyard, leaving behind her infant child, the discovery turns everything Helena believes about elves on its head. In the conflict between elves and humans, one innocent child may shift the balance of power-and force Helena to make the most difficult choice of her life.