Patricia Pettit Hill 
Ishi, Deshi and Hank [EPUB ebook] 
Discovering Bigfoot

Ishi, Deshi, and Hank first meet at a campground in Michigan. Ishi is the fifteen-year-old son and only child of a husband and wife from Boston. Deshi is the ten-year-old adopted son of two men from New York City. Hank (Henrietta) is the fourteen-year-old biracial daughter of a single mother from Chicago.
Being the only children at the campground, they soon find themselves in the pursuit of a mysterious bigfoot creature as they experience strange sightings, time loops, and dimensional shifts. They get lost in a cave that becomes a passage to France, where they meet two new friends. The three finally discover the bigfoot and eventually learn everything about the shape-shifting creature.