In Australia’s Great Barrier Reef, a clownfish named Marlin and his wife Coral take up residence in an anemone at the edge of the coral reef. Although Marlin frets that his four hundred as-yet-unhatched children will not like him, Coral assures him that he will be a wonderful father. Just then, however, a barracuda attacks the anemone, knocking Marlin unconscious, and he awakens to discover that Coral and all the eggs, except one, have been eaten. Cradling his remaining son, Nemo, Marlin vows to protect him forever. Soon, Nemo is a happy, curious boy, who lets neither a malformed fin nor his father’s overprotectiveness dampen his energy. On Nemo’s first day of school, Marlin embarrasses him at the schoolyard by anxiously fussing over him and insisting on cautiousness. To prove that he does not need coddling, Nemo accepts the other kids’ dare to swim out to a ship just past the reef drop off. Although he bravely swims into the open sea, which his father has taught him is perilous, touches the boat and turns back in triumph, a scuba diver nets him before Nemo can reach safety. Horrified, Marlin rushes to his son’s aid, but the boat speeds away too quickly for Marlin to keep up with it, and when he begs for help, only a cheerful blue tang named Dory responds. She offers to help him follow the ship, which she saw pass by, but after several minutes, Marlin realizes they are swimming aimlessly. As Dory explains that she suffers from short-term memory loss, a menacing shark named Bruce forcibly escorts the pair to a twelve-step meeting designed to cure fish-eating addictions. Chanting “Fish are friends, not food,” the three group members welcome Marlin and Dory, and while Bruce recounts the tale of his father’s abandonment of the family, Marlin spots a diver’s mask and, sure it belongs to the human who captured Nemo, inadvertently cuts Dory in his excitement. The scent of her blood mesmerizes Bruce, who chases the fish into a wrecked ship, and although Marlin and Dory escape, the chase sets off a mine explosion. Meanwhile, Nemo is transported to a fish tank in the Sydney office of dentist P. Sherman. The other aquarium inmates, including Jacques the shrimp, Deb, a starfish named Peach and Bloat the blowfish, welcome the boy, but when he becomes stuck in a filter, their gruff leader, Gill, insists that Nemo escape without help, demonstrating his own damaged fin as proof that a handicap need not impede him. The tank members soon “initiate” Nemo into their society and form an escape plan to save Nemo from being given to the dentist’s niece, Darla, a notorious fish abuser. Gill’s plan calls for Nemo to swim into the filter and jam it with a pebble, after which the dentist will clean the tank, transferring them to plastic bags in which they plan to hurl themselves out the window and into the harbor below. Back in the sea, Marlin swims, with Dory’s encouragement, to the ocean depths to find the fallen mask. In the dark, both are spellbound by the light of a predatory angler fish, but manage to spot the mask. While Marlin distracts the angler, Dory slowly reads the dentist’s address on the mask, and is thrilled to discover that she can remember it. Soon annoyed by her blithe chatter, enthusiasm and memory lapses, Marlin informs Dory that he would like to travel alone, and her subsequent sobs attract the chivalry of a school of fish, who scorn Marlin but provide Dory with direction to the Sydney harbor. Now aware that he needs Dory’s help, Marlin apologizes and swims off before he can hear the school’s advice to avoid the upcoming trench. Although Dory tries to warn Marlin, she forgets the details and follows him above the trench, which serves as a jellyfish bed. Marlin is resistant to the stings, but Dory is not, so to save his oblivious friend, Marlin pretends to play a “game” with Dory in which she bounces harmlessly over the jellyfish tops, thus avoiding the dangerous tentacles. Before they reach the end, however, Dory is stung and lies unconscious. As they both recover in open waters, Nemo continues his getaway attempts, sure that his timid father would never risk the open water to rescue him. He fails to achieve the dangerous task, however, and the tank fish sink into dejection. Meanwhile, Marlin awakens on the back of a sea turtle named Crush, who explains that his school is riding the East Australian Current into Sydney. Dory is nearby, playing games with the turtle children, including Squirt, whose independence while swimming the rapid current impresses Marlin. The youngsters idolize Marlin, as does Dory, as she listens enraptured to his tales of their own travels through the ocean. Marlin’s astounding stories soon spread throughout the ocean until they reach the pelicans in Sydney Harbor, one of whom, Nigel, regularly visits the dentist’s office and recognizes Nemo’s name. When he informs Nemo of his father’s courageous search, Nemo is overjoyed and, inspired, flings himself into the tank filter and jams it. At the same time, Marlin and Dory leave the turtles to brave the current alone, and Marlin finds himself invigorated by the adventure. They swim toward shore but are soon lost in the vast ocean, and after Dory tries to ask a whale direction in its own language, the whale swallows them both. Inside its mouth, Marlin rages at his friend. After he states that he must keep his promise to Nemo never to let anything happen to him, Dory points out that this promise cannot be any fun for the child. Dory then assures Marlin that the whale has told her “it’s time to let go,” and although Marlin is frightened, he does so, allowing the whale to expel them via his blowhole into the harbor. The next morning, the tank fish awaken to discover that a new filtration system has cleaned the aquarium. The dentist then nets Nemo, and although the others try to wrench him free, the dentist succeeds in capturing Nemo just as Darla arrives. Outside, a pelican tries to eat Marlin and Dory, whose struggles attract the attention of Nigel. Upon hearing Marlin say Nemo’s name, Nigel offers to carry them in his mouth to the dentist’s office. Marlin is suspicious, but when hungry seagulls approach, he readily agrees. They reach the office in time to see Nemo feigning death, hoping to be flushed down the toilet, as Gill has assured him that all drains lead to the sea. When Darla grabs Nemo, Gill jumps onto her head, and pandemonium erupts in the office. Soon, the dentist is unconscious and Gill has sacrificed his own chance for escape by tossing Nemo down the spit bowl. As Nemo is flushed into the Sydney water treatment pipes, he calls for his father, who is despondent at this missed opportunity to save his son. Believing Nemo to be dead, he mournfully bids goodbye to Dory, and when she begs him to stay with her so she can continue to regain her memories, Marlin states that he wants only to forget his. Soon, Nemo struggles out of the pipes, and although he meets Dory, she fails to remember that she is on a quest to find him. Suddenly, however, her memory returns, and she brings Nemo to his father, who embraces him joyously. Within moments, the trio is caught up in a fisherman’s net along with a huge school of fish. Marlin tries to hold Nemo back but finally relents when the boy asserts that he can remedy the situation, coaching the fish to swim downward as one. The combined force of their movement breaks the net from its rope, and all are freed. When Marlin searches for Nemo, however, he finds him dazed beneath the fallen net. Marlin cradles his son, who soon regains consciousness. Later, back on the reef, Marlin urges Nemo to get to school on time, and once there, jokes easily with the other fathers, proud to see his son leave to explore his ocean home. At the same time, the tank fish achieve their goal and throw themselves into the ocean, where they float in perfect happiness, though still unsure how to escape their plastic bags.