Hanne, Marthe and Julia have the vacation of a lifetime in the coastal village of Porto Sirento. But when a mysterious spell turns the girls into beautiful mermaids, their holiday is turned upside down. The inhabitants see mermaids as monsters, so they have to avoid water at all costs! But that is easier said than done..

A worker from the company 'Onze Jongens', which has gone back to normal handyman work, sees an opportunity to get out of debt.