Millions of years after its separation from Earth, Planet Mamango is approaching once again. Private investigator Ban Shunsaku stumbles upon a murder case and encounters researcher Shikishima Kenichi, whose knowledge holds the key. Shikishima reveals that an energy-producing stone from Planet Mamango exists, and armed with this knowledge, he builds a rocket to embark on an expedition. Along with a team consisting of Captain Butamo Makeru, Ayame, Momiji, Mii the rabbit, and Ban Shunsaku himself, Shikishima leads the charge towards the planet only to land in an ancient landscape swarming with prehistoric creatures and lush flora, known simply as "The Lost World."
