After receiving a clue from Fujiko, Lupin and his gang go searching for a legendary undersea treasure in Kiritappu, Japan. Quick enough, Inspector Zenigata chases them from the dig site and up the road to a strange lighthouse, where they are met by a strange figure calling himself "Mamou." Mamou clearly has it out for Lupin, and after a bit of a light show, sends Lupin, Goemon and Jigen 500 years into the past, with Zenigata right behind them. Now the trio is caught up in a land war between two ancient tribes, and are forced to solve the mystery of the legendary treasure as the time-traveler Mamou threatens to remove Fujiko from existence by erasing her ancestor!