Set in a beautiful coastal town in the Italian Riviera, the film tells the coming-of-age story of a boy named Luca (voiced by Jacob Tremblay) during an unforgettable summer filled with gelato, pasta and endless motorcycle rides. Luca goes on an adventure with his best friend Alberto (voiced by Jack Dylan Grazer) and his new friend Julia (voiced by Emma Berman), but all the fun is threatened by a deep secret - the two of them are sea monsters from another world beneath the water.