Tremolo: cry of the loon, by Aaron Paul Lazar. Most likely this is part of the Read an Ebook Week promotion.
Book Description
In this coming-of-age mystery set in the Belgrade Lakes of Maine, young Gus LeGarde witnesses a girl being chased through the foggy Maine woods. She's scared. She's hurt. And she disappears. Tremolo is a stirring and nostalgic trip back to summer, 1964, in which Gus faces his deepest fears while solving a baffling mystery.