The little fish Nemo lives on the Great Barrier Reef off the coast of Australia. He is caught by a dentist and transferred to an aquarium in the dental office. The other fish in the aquarium comment when the dentist is performing operations. A starfish announces: 'We got a live one. A root canal, and by the looks of those X-rays, it's not gonna be pretty.' The dentist begins to use an air rotor and the patient starts screaming. The boxfish mumbles 'Rubber dam and clamp installed?' The starfish confirms and then reports that the dentist uses a Gator-Glidden drill and seems to be favouring that one lately. The dentist introduces an endodontic file after which the patient screams again. A fish mumbles 'now he is doing the Schilder technique'. Next, two other fish start quarrelling about whether the dentist uses a Hedstrom file or a K-flex. At that moment a pelican flies next to the window. The starfish tells the pelican that he has missed a root canal treatment with a Gator-Glidden drill. The Pelican agrees that the dentist seems to be favouring that one and says 'Hope he doesn't get surplus sealer at the portal terminus...'. After the dentist has scared the pelican away, he turns to his patient, saying that he is 'going to see a man about a wallaby,' and disappears to the bathroom.

On a subsequent visit, the pelican appears again at the moment when the dentist is performing an extraction. The dentist is distracted and with one single move he removes the tooth, causing the patient a lot of pain. The dentist explains simply: 'That's one way to pull a tooth. Well, good thing I pulled the right one, eh, prime minister?' The pelican, who has missed the extraction, asks the starfish whether the dentist has loosened the periodontal ligament already.

At the end of the film, Nemo escapes to the spittoon next to the dental chair and travels through the sewage system to the ocean, where he is reunited with his father.