Lost King by Lola Gabriel

A dark threat purses them at every corner. To live, they must learn to work together.

Sabine is the legendary Winterfox, the daring and mysterious vigilante who operates without the help of the law. When her identity is discovered, her life falls apart and she finds herself kidnapped.
When she’s rescued, she doesn’t know what to expect. Soon, she finds herself in the custody of the Lost King, a powerful, enigmatic man who never shows his face, but carries out justice for those powerless to defend themselves.
As things continue to go wrong, Sabine becomes stranded with the Lost King in a situation where they either have to work together or die separately. She learns more about this secretive man and why he is so afraid to take off the mask. She finds herself beginning to have feelings for him, feelings that are as raw as they are undeniable. But, can they every find happiness when a dark threat pursues them at every turn?