A cautious clownfish named Marlin lives in the Great Barrier Reef, left overprotective after a traumatic event that left him as the sole guardian of his only son, Nemo. Desperate to protect Nemo from the ocean's inherent dangers, Marlin's fears are realized when Nemo, rebellious and yearning for independence, is unexpectedly captured by a diver and ends up in the fish tank of a dentist's office in Sydney. Faced with his worst nightmare, Marlin embarks on a perilous quest to rescue his son, proving that the ocean's vast and unpredictable expanse is no match for a father's love.

Along the way, Marlin encounters a forgetful but spirited regal blue tang named Dory, who despite her short-term memory loss, becomes his stalwart companion. Together they navigate a series of adventures and misadventures, braving dangerous waters and meeting a host of quirky sea creatures. Their journey takes them through environments fraught with menace, including an encounter with sharks who have sworn off eating fish and a perilous swim through a jellyfish field. As they push forward on their quest, Marlin learns valuable lessons about trust, letting go, and the power of an unwavering determination when fueled by love for one's family.