The Mostly Invisible Boy by AJ Vanderhorst | Review
Eleven-year-old Casey is stubbornly friendly, but he's eternally the new kid at Vintage Woods Middle School. Students look right through him—and they're not faking. Casey doesn't know why he's mostly invisible, but when he scales a colossal oak, he discovers a fortress in its branches. The forgotten sentry tree marks the border between his safe, suburban life and a fierce frontier.