The Island of Beyond — Elizabeth Atkinson

Eleven-year-old Martin can hardly imagine a worse summer. Martin's dad wants him to like "normal" boy things -- playing sports and exploring the outdoors -- so he sends Martin to his great-aunt Lenore, who lives on a tiny island called Beyond. Nothing about Beyond is what Martin expects, certainly not the strange, local boy who unexpectedly befriends Martin. Solo can canoe and climb trees and survive on his own in the wilderness, and Martin's drawn to him in a way he doesn't quite understand. But he's not sure he can trust Solo. In fact, can he trust anything about this strange island, where everyone seems to be keeping secrets?