Kaito, Rena, and Taki are swept away by a whirlpool and end up in a cave. They see an underwater city full of life force. The city guards catch them and confiscate Kaito's Dino Dagger. While Kaito and Rena escape, the run into a girl named Helen tells them they are in Atlantis. Meanwhile, Diamond Ryugu sends the Drago Clones to the city. Helen helps Kaito get the dagger back, but they must stop the Drago Clones.
