The Secrets of Spirit Island

Jack lives on the Minnesota and Canada border. His grandpa and father are lumberjacks, working for a big lumber company. His best friend is a big yellow Labrador dog named Duke, who plays an important part in his life.
An Oriental family from China moves to their neighborhood. Phan becomes his best friend, and Phan's father teaches them ninja. During one of their adventures, Jack finds a cave on the side of the mountain where ancient medicine men live, who teach him the secrets of the island.

As the years go by, he marries his girlfriend, Jessie, and they have a family. Jack is drafted into the service and is sent to Vietnam, where he uses the secrets the old medicine men taught him.