Trama

On the Italian Riviera, an unlikely but strong friendship grows between a human being and a sea monster disguised as a human.

A 13-year-old boy experiences an unforgettable seaside summer on the Italian Riviera filled with gelato, pasta and endless scooter rides. Luca shares these adventures with his newfound best friend, but all the fun is threatened by a deeply-held secret: he is a sea monster from another world just below the ocean's surface.

Young Luca and his best friend, Alberto, summon up the courage to visit the picturesque fishing village of Portorosso. However, the boys share and hide a great secret: they are not ordinary children but harmless sea monsters who live underwater, eager to find out what lies above the sea's surface. Before long, adventure after adventure and experience after experience, the two wide-eyed explorers will discover the true meaning of freedom, the importance of family, and the catalytic power of acceptance.—Nick Riganas

Set in a beautiful seaside town on the Italian Riviera, the original animated feature is a coming-of-age story about one young boy experiencing an unforgettable summer filled with gelato, pasta and endless scooter rides. Luca shares these adventures with his newfound best friend, but all the fun is threatened by a deeply-held secret: he is a sea monster from another world just below the water's surface.—Pixar

Luca Paguro is a pre-teen sea monster living off the coast of the Italian city of Portorosso who spends his days herding a school of fish. His parents, Daniela and Lorenzo, restrict him from going to the surface out of fear, but doing the same thing day after day ends up making Luca bored. One day, while feeling conflicted about whether or not to go to the surface, Luca meets another young sea monster named Alberto Scorfano. Alberto has been on land many times and has a hideout on an island near Portorosso where he claims he lives with his father. He begs Luca to follow him there. Reluctantly, Luca follows, and they transform into humans on the dry land and make their way to Alberto's hideout. Luca finds a poster in the hideout showing a Vespa, an Italian scooter, and they soon decide to make their own from scratch. All the while, Luca tries to keep his now double-life a secret from his parents with only his grandmother being clued in and keeping it a secret.

Lorenzo and Daniela soon discover what Luca has been doing and decide that to keep Luca safe, he should be sent deeper into the ocean to live with Lorenzo's brother Ugo. Distraught, Luca runs away to the city of Portorosso with Alberto. There, they learn of the local bully and repeat champion of the Portorosso Cup Race, Ercole Visconti. Just as Ercole is about to dunk Luca's head into a fountain which would expose his identity as a sea monster, he is saved by a young girl named Giulia Marcovaldo. Giulia takes Luca and Alberto to her house where she lives for the summers with her one-handed father Massimo, an expert fish hunter seeking to kill a sea monster.

Meanwhile, Daniela and Lorenzo are unable to find Luca anywhere, so they decide to go up to the surface to locate him. They begin splashing water on all of the boys there in an attempt to find Luca.

Luca, Alberto and Giulia decide to enter the Portorosso Cup Triathlon together in hopes of winning money to buy a Vespa. The triathlon consists of three races: swimming laps, eating pasta, and riding a bike through the town. Each child decides to take up an individual task: Giulia takes up swimming, Alberto takes up eating pasta, and Luca takes up riding a bike after learning how. Over time, Ercole starts to become suspicious of the boys, and Luca and Giulia start to become closer to each other. When Giulia talks about going to school in another part of Italy where she spends the rest of the year, Luca develops an interest in it. Alberto becomes jealous of Luca and Giulia's growing friendship. After an argument, Alberto reveals his identity as a sea monster to Giulia. Luca does not do the same and instead acts afraid of Alberto, leaving Alberto to retreat to his hideout feeling betrayed.

Back at Giulia's house, Giulia spills water on Luca, exposing him as a sea monster. Giulia sends him away, worrying that someone could hurt Luca if his true identity was discovered.

Luca finds Alberto in his hideout sulking. After Luca questions Alberto about tally marks on the wall, Alberto reveals that he made the marks counting the days since his father left him there alone. Alberto is still mad at Luca and no longer wants to be a part of the triathlon, but Luca decides to enter with Giulia anyway.

On the day of the triathlon, Luca and Giulia arrive without Alberto. After completing the first two challenges successfully, they enter the cycling stage. It begins to rain and Luca tries to avoid being turned back into a sea monster by stopping his bike under an awning. Alberto arrives at the scene with an umbrella to help Luca, but he gets wet and is transformed back into a sea monster. Ercole throws a net, trapping him. Risking his secret being exposed, Luca runs into the rain to save his friend. He frees Alberto but also gets transformed. Giulia tries to stop Ercole from hurting them but she ends up getting hurt herself. Luca and Alberto carry her back to town. When they get there, Ercole tries to kill Luca with a spear, but Luca puts the bully in his place. Everyone in the town of Portorosso sees that the sea monsters are not actually bad, especially Massimo, who thanks the boys for helping his daughter. Luca is reunited with his parents and they celebrate at Giulia's house.

Later, Alberto reveals that he sold the Vespa they bought with the prize money to buy a train ticket for Luca to go to school with Giulia. Luca's family, Massimo, and Alberto (who has decided to stay in Portorosso) all see Luca and Giulia off at the train station. Luca waves goodbye to them and becomes a sea monster once again as the train travels away into the rain.