The Forest of Stolen Girls

The why of the mystery is fairly straightforward, but the who of the mystery was a twisty path that didn't really end where I expected. The relationship between the sisters and their relationship to the island is a strength of the story. Visiting ancient Korea was interesting, but the story felt fairly universal in a lot of ways.
So if you are looking for a story about sisters overcoming hard feelings and bad guys, you will enjoy this story.