Copper, Charli, and her six-year-old ghost friend, DJ, are so excited to stay with their Nanna and Pop at their beach house for a few weeks. One day when Charli, DJ, Copper, and their friends decide to swim at a lake, they discover a willow tree that holds an exciting secret. When they decide to climb the tree, a round door suddenly appears. After Charli, DJ, and the others decide to investigate, they are transported to a water park that holds a great adventure with cool sea animals who soon show them how much fun can be had with just a little magic. In this thrilling tale, a group of children travel through a door in a magical willow tree where they find friendship with beautiful sea creatures living in an underwater world.