The Cairn in Slater Woods — Gina Rosati

Dylan has just moved to New Hampshire to live in a house his family has inherited from a great aunt he's never met. There he meets his cousin, a bully who resents Dylan's family, and a mysterious girl who claims she can lead him to buried treasure in the woods on the property. The key to helping the girl involves uncovering a dark family secret and righting the wrongs of the past.