The Secrets Below by Camilla Sten

What happened out there in the woods?

Twelve-year-old Tuva couldn’t imagine living anywhere other than the Stockholm archipelago and her island home of Harö. Even if she mostly keeps to herself at her small school. Even if she sometimes gets kind of lonely.
But when a classmate goes missing, Tuva finds herself at the center of the mystery, along with Rasmus, the new boy at school. Neither one of them can understand what they saw that day in the woods near the water: Is something magical at work? Something evil?
And it’s not just their classmate who has gone missing. Other people around the islands have gone missing this fall, disappearing from their boats on the water, never to be heard from again. Can Tuva and Rasmus discover what secrets are lurking below…before it’s too late?