Piet, Berend and Stien are ready to sail out of the harbour with their ship the Scheve Schuit. But suddenly they hear a siren song. Stien recognizes the voice immediately; it's the voice of a mermaid! According to an old book that Stien received from Steven, mermaids live in Atlantis. So, if they can hear that voice, Atlantis must be very close! Berend and Stien want to look for that mermaid and the treasure of Atlantis. The pirates dive into the water and experience an exciting adventure, toget...