A new 20th century museum has opened in Khazu City! Looking like a striking replication of the 1970 World Expo, the museum quickly wins over the hearts and minds of the adult population. It becomes clear to Shin-chan that the designers of the museum have ulterior motives as all the adults flock to the museum and lose their memories, returning to the comfort and nostalgia of the 20th century. It's up to Shin-chan and his friends to unravel this heinous plot and return their parents to the 21st century before the whole world follows them into the past!