It's time for the summer sunshine and nine year-old Elisabeth Vanklewen and her best friend Eveline Brighton are ready. With a kids sandcastle contest that their town has organized and some tough competition, the castle building is going to be ""sandtastic"", for ""shore"". But when there are some 'fishy' goings on along the beach, it seems like the friends have another mystery to solve. After some ""sandsational"" sleuthing it becomes clear that only Elisabeth and Eveline (The Clue Duo) can solve the case. Join Elisabeth and Eveline along with their classmates, Brad and Colin, as the Clue Duo solves the case while having some fun in the sun.