Wicked Savior by Stella Brie

When the archangel Gabriel sends his angels to eliminate a woman, Lucifer knows she’s the critical pawn in his quest for revenge. Intent on pushing Gabriel to the edge of his sanity, he assigns himself as her protector.
A scientist, Evren is focused on two things: finding her mother and helping the nearly extinct Druids. She isn’t interested in being a pawn, nor does she need Lucifer’s protection, even if he intrigues her.
But Druid history is shrouded in secrecy and finding the answers she seeks takes time. Too much time. Evren soon discovers playing god has consequences, and she can’t save the world alone.
Lucifer and Evren race to eliminate the threat before Gabriel succeeds in his attempts to kill her. And when Evren’s greatest secret is revealed, Lucifer realizes he will do everything in his power to protect the woman he’s falling for, even if it means going to war against the angels.