In the deep sea of Australia's Great Barrier Reef, clownfish father Marlin and his son Nemo live a simple, happy life. However, the father is often timid and hesitant in his actions, a bit of a coward, which makes Nemo feel that his father is not brave at all—he even looks down on him a little. Little Nemo, on the other hand, fears nothing. While playing near the surface with his friends, he gets caught in a fishing net and ends up being sold to a dentist's clinic. Marlin is deeply worried about his son's uncertain fate. Even though he is usually not one to act boldly, for his son's sake, he musters the courage to venture out. Yet along the way, he encounters many hardships and fears that make him terribly anxious. Fortunately, he meets the kind-hearted Dory, who accompanies him on his journey. Both father and son receive help from many warm-hearted individuals along the way, and they eventually reunite. From then on, Marlin becomes a hero in the eyes of his son and everyone else.