Agnes Mallory by Andrew Klavan

A chance encounter in the woods causes a recluse to dredge up old memories

He meets her in a stranger’s backyard. Harry is a child walking home from school, and Agnes is a young girl playing in the creek behind her house. While their parents speak, the children play, and Agnes explains the supernatural. She uses cookie dough to make statues of ghosts, she tells him, which she sets free in the river. So begins an enchantment that will last the rest of Harry’s life. 

Years later he is a disbarred lawyer, living a reclusive life outside a Westchester commuter town. Memories of Agnes, dead for a decade, haunt him. He befriends a shivering young runaway, an encounter which forces him to confront his past for the first time, unearthing a mystery which stretches back to the Holocaust, and revolves around that strange young girl he met so long ago.