When Owen and his distracted older sister are alone and their parents are away, Owen delivers the paper, dodges a school bully, and spends afternoons in a forest hideaway making tall tales, and making inventions. When he encounters three thugs and a mistreated dog, his life changes. Owen frees the dog and bonds with the golden retriever. When he reads a newspaper account of a diamond heist, he realizes that the thugs are the chief suspects and he suspects that the thugs hid the diamonds on her collar. Owen changes the dog's name to Diamond. He takes her to the police and the police think that the story is not true. The thugs are in pursuit of the diamonds.