Ian is an architect who loves imagining new places. One day, on his birthday, he realizes that he hasn’t heard anything from his uncle, Uncle Henry. Worried, Ian sets off to find him, traveling by bus, train, airplane, cruise ship, and submarine.

Along the way, Ian visits the extraordinary houses he has built for his uncle: a maze house, a cactus house in the desert, a jungle house, and an ice house on Snow Island. His journey leads him deep into the ocean, where he takes a small submarine and discovers a giant octopus holding his uncle’s submarine tightly in its enormous arms. Using light, Ian rescues Uncle Henry from the octopus.

Together, Ian and Uncle Henry travel into space to meet aliens. They bring gifts from Earth—sand from the desert, a jungle flower, a piece of ice from Iceland, and coral from the deep ocean—all carefully packed in a box. Seeing these treasures, the aliens admire Earth's beauty and begin to dream of living there one day.

In the end, Ian imagines and builds a new amusement park shaped like an octopus in outer space. The aliens love this extraordinary place, where they can play, meet humans from Earth, and share their worlds together.