During a lake trip, the Pixies, because of Cherie's sudden mood swing, are sucked into a vortex and are taken in the Mermaids' underwater world. The Mermaids' city is threatened by a fierce water creature that devours the Flux, the same precious element, which the mermaids' city is built with. The Pixies help their new Mermaid friends - Redne, Ayca and Li-ban - to knock the monster out to the music's rhythm!