Ken is a young boy brimming with adventurous spirit who uncovers a mysterious egg within an automobile factory or junkyard. Hearing cries emerge from the egg, he approaches and witnesses the hatching of a unique yellow car-like creature named Bumpety Boo. Ken immediately intervenes to shield the newborn from crushing machinery, forging a strong bond between them.

Initially working at a church, Ken's precise family background remains unclear, though not explicitly confirmed as orphaned. He nurtures a personal dream of owning a car, a dream unexpectedly realized with Bumpety Boo. Learning of the creature's deep desire to find its mother, Ken boldly initiates a global journey to aid in the search.

Throughout their expedition, Ken embraces adventure with an eight-year-old's boundless enthusiasm, frequently steering himself, Bumpety Boo, and their dog companion Mopsy into unpredictable situations. Traveling far and wide, they consistently assist those they meet, including rushing a pregnant woman to the hospital and rescuing a lost baby elephant, ultimately reuniting it with its mother despite initial confusion.

Ken gradually becomes aware of Professor Honky-Tonk's persistent efforts to capture Bumpety Boo, initially encountering the professor in various disguises. This awareness transforms into active evasion of the professor's escalating schemes as the journey unfolds.

Their worldwide quest culminates successfully with Ken helping Bumpety Boo finally locate its mother, achieving the central purpose of their extraordinary expedition.