Ugo, an Angler-like sea monster, is off-putting to Luca, and he escapes his house. To teach him a lesson, they plan to send him away to live with Uncle Ugo, Lorenzo's brother, in the deepest depths of the ocean and keep him away from the surface. His parents catch him and reveal that they have found the human objects he has accrued. Luca awakens to realize he overstayed his welcome and rushes back home. Luca has a wonderful dream of riding his Vespa with Alberto and flying into the sky to see the fish, but it ends with it raining and Luca turning back into a sea monster. However, the experience livens Luca, and later at night, he witnesses stars for the first time, though Alberto informs him that they are glowing fish that fill the sky. Alberto then informs him that he needs to declare 'Silenzio, Bruno!' to encourage himself, and they ride down the hill and off the ramp before crashing into the water. Eventually, Alberto convinces Luca to ride the hill down with him, but he is too scared. Meanwhile, Daniela and Lorenzo put together that Luca has been swimming off somewhere and become concerned for him. Unfortunately, the scooter falls apart, but Alberto is more determined to build a better one, and he and Luca spend the next couple of days collecting and rebuilding Vespas. Luca is forced to hold the ramp while Alberto rides it. The next day, Luca and Alberto try out their scrap scooter by riding down the island's hill. They spend a couple of hours perfecting it before Luca realizes he needs to return home. Alberto explains that it is a vehicle that can take you anywhere Luca becomes entranced with the idea of owning one and traveling the world and suggests that they take the junk that he has collected to build one.

Next, Alberto takes him to his hideout, a tall abandoned tower, and shows him all the things he has collected, including a poster for a Vespa, an Italian scooter. Luca is mystified at having legs to stand on, and Alberto gives him a quick lesson on walking. Luca soon becomes attracted to going back to the surface, and Alberto eggs him to come up. He is confronted by Daniela for being gone for a long time, but Grandma protects Luca by claiming that she sent him out to get sea cucumbers. Scared but amazed, Luca returns to the ocean.

He forces Luca up to show him what it is like and discovers that he transforms into a human when he hits dry land. The diver turns out to be another sea monster named Alberto Scorfano, who had been collecting the items to begin with and taking them back to his hideout on the surface. The next day, Luca follows a trail of more human objects until he is cornered by what looks like a deep-sea diver. On the other hand, his grandmother openly discusses her adventures on the surface in the past and seems supportive of Luca wanting to get out.

His mother, Daniela, is highly protective of him and warns him of being caught by anyone from the surface, while his father, Lorenzo, is slightly inattentive and distracted. Luca, bored with his simple life, takes notice of a clock and a joker card that he found on the ocean floor. Luca Paguro is a sea monster who farms goatfish for his family in a hidden area of the ocean. Upon seeing it, they recognize it as a sea monster and try to catch it, but it escapes, much to their dismay. Two fishermen, Giacomo and Tommaso, are out at night trying to catch fish when a strange creature suddenly begins swiping things from their boat. Luca shares these adventures with his newfound best friend, but all the fun is threatened by a deeply-held secret: they are sea monsters from another world just below the water's surface.

Set in a beautiful seaside town on the Italian Riviera (Liguria), Disney and Pixar's original feature film Luca is a coming-of-age story about one young boy experiencing an unforgettable summer filled with gelato, pasta, and endless scooter rides.

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