Summary -- Part I: Geraldine Chaplin writes an inspirational letter. Dad Scott tells son David to stop complaining about flying and, in a small plane, half-brother David takes the controls while Dad sleeps. A storm forces a crash-landing in water. Dad is stuck in his seat-belt (kids, take note) and presumably drowns as the boys swim ashore. They soon see a cave shaped like a dinosaur head and it blows up. The guy from The Island of Dr. Moreau emerges, identifies the place as Dinotopia (about 200 miles across), and introduces himself as Cyrus Crabb, archaeologist. There are no cell phones; they'll have to use a "postal bird." They trek to a village in order to catch a bus to Waterfall City. A plated dinosaur rampages but a woman named Marion calms it and extracts a tooth, alleviating the toothache that caused the rampage.

The next morning the half-brothers and Marion climb onto an armored brachiosaur (the "bus"). "He won't eat us, will he?" "Brachs are plant-eaters," replies Marion, but the creature is armored because they have to pass through the rainy basin, the domain of the carnivores. Marion notes that the carnivores "aren't evil; they're just hungry by nature." Dinotopia does not believe in weapons, but there are disturbing signs that the tyrannosaurs are hunting in packs. An outpost is deserted and its sun-stone has failed, but they must stay there the night. Idiot-boy wants a burger or some chicken to eat. Marion discusses vegetarianism briefly, but a T-rex attacks. Another clashes with it. "Skybacks" help (pterodon-flying soldiers).

The next day Karl continues being a jackass: "C'mon, Marion, eat or be eaten, kill or be killed -- that's the law of the jungle" with man "at the top." Marion says that dinosaurs teach humility. Marion's father is Waldo Seville, the Mayor of Waterfall City where they all finally arrive. The brothers learn that they cannot get off the island and that the last "off-worlders" to arrive were shipwrecked on the shores in 1944. David babbles unorganizedly about world events since but the Dinotopians scoff at the idea of the Apollo 11 moonwalk.

At an ancient library they meet an English-speaking dinosaur named Zippo whose soulmate Sylvia is dead. David identifies Dinotopia as a utopia but clashes with the hotheaded Karl over the sanctimoniousness of dead Dad. The Mayor gives Marion a letter from her grandmother insisting that she "find the light," and a sun-stone amulet.

Crabb slowly is revealed as a malcontent in his discussion with Karl. The children of Dinotopia learn the Code: "Others first; self last," etc. Marion teaches Saurian and reveals a bit about the World Beneath where dinosaurs found sanctuary in mythic history. The 11th code begins with "fin-." Karl is quickly fed up and quits school but David sticks it out. Karl kicks Zippo's ass at pingpong.

David and Marion visit the sun-stone that powers Dinotopia. Later, the brothers clash again: Karl thinks David is brainwashed; David thinks Karl is being negative. Karl visits Crabb who says there might be a way to escape if he could get his hands on a secured book. He shows a torn leg and alludes to an incident involving an ancestor of his and a fire. But Karl must steal the log of the Rebecca's Folly from Zippo, which he does during a ceremony honoring Marion and involving fireworks. He makes an educational deal with Marion and brings the book to Crabb, who now says they need to retrieve something from the shipwreck. Karl plagiarizes Queen's "Bohemian Rhapsody" to pass the Saurian exam. David argues with him and says that Dad was worthless, so they fight, fall into the falls, and are swept downstream.

Marion and Zippo search with the help of a mail-bird. Karl escorts a weak and hurt David to an ancient and ominous temple. The search party finds them and Zippo sends the bird for a rescue party. Zippo is excited about this lost temple and thinks there's a connection with the mythic half-human/half-dinosaur leader of the World Beneath, but the entrance to such a place ought to be guarded by carnivores. It is: in the swamp lurk alligator-like creatures which now attack. Zippo is temporarily dragged under but escapes with the rest.

Summary -- Part II:

We all visit the Matriarch on a farming commune (except that there's a Matriarch) where dinosaurs serve as oxen. She's Rosemary, Marion's mother, worried about the carnivores straying and not convinced that David is the emotionally stable brother after all. Zippo improves slightly at ping-pong and brings life-prolonging tea to David. Karl rankles at working and sneaks off with Marion at night for a swim, prompting tension at the communal dining.

Zippo reports back to the Senate at Waterfall City about the ancient temple, one of three entrances to the World Beneath, but he's met with disapprobation -- despite the hope of finding sun-stones, it's trespassing on carnivore turf. Meanwhile, back at the farm, the post-harvest cult ritual of four hours silence and getting in touch with the earth affects even Karl.

Farmhands receive their diplomas and posts: Karl, being "of the land," to the hatchery; and David, "of the sky," to Canyon City for Skybacks training. Marion has no habitat, and Momiarch sends her with David to study something. The two bid a smirky good-bye to Karl. Ramana, overcompensating for who knows what, greets David among the eyries. Skybacks cannot descend beyond a certain point, and training begins. Marion's younger sister brings Karl to the incubation room and introduces him to egg #26, his assigned saurian life partner.

Crabb alarms the town meeting over the dying sun-stones and demands library access. He chums up to Zippo, who begins translating ancient documents until he realizes Crabb's shop is littered with stolen items. Crabb conks Zippo and dumps him in the sewer. Meanwhile, training and hatching take place. A couple pterodons attack Marion, but not fatally. Karl restores a boat which Crabb sabotages, making a swap of a navigation chart for a stolen sun-stone, but Karl cheats him and the baby dinosaur, 26, jumps in the water after Karl, who returns and rescues the creature.

In true dinosaur movie tradition, we get "rockclimbing"! David and Marion ascend to a nest where David's love proclamations are interrupted by the mail-bird with a singing telegram from Karl. David names an albino pterodon "Freefall." At the final saddling ceremony, David is at first rejected but later Freefall gives him a daring ride.

Summary -- Part III:

Refugees pour into Waterfall City as our heroes plan a clandestine trip to the swamp temple. Zippo will babysit 26. Crabb tries to connect with Karl again and gives him a flare gun, and fraternal jealousy over Marion continues. In the caves, when Karl fires the flare, hundreds of bat-osauruses -- okay, pterodons -- get stirred up. The humans flee and are arrested for breaking all the laws of Dinotopia (which seems unlikely since there are about 56,000 of them). The Mayor presides at the trial. Zippo tries to help but doesn't. The Skybacks Captain does, and the Matriarch testifies to the boys' fine natures. Karl pleads for the release of David. But 26 is to be sent to an orphanage and their education is to continue. (So the message is that education is punishment. Swell.)

With the log of the Rebecca's Folly and the Journal of Arthur Denison, Crabb could help. Denison and Crabb's father Lee were the discoverers of the World Beneath. Lee Crabb was tried and punished, prompting Cyrus' 20 years of "study." He convinces Marion to drug the guards and Zippo to steal the maps of the caves below. Crabb has a gun and his father's submarine. The boys escape and take a wild Disney water-ride to Crabb's father's storehouse. Crabb limps about with a harpoon (quel Ahab!). We need Marion's sun-stone to power the sub, but she is left behind.

Over 100,000 pteranodons are about to terrorize Waterfall City and the prime sun-stone is failing. Marion must lead them all in prayer at "Fountain Square" (Cincinnati?). Meanwhile, underwater, the three guys see Dad's plane empty. They surface and see the remainder of the carved Code: "[Fin]d the light." (That's it? What a gyp!) They read hieroglyphs indicating the history of the place, involving a meteor and a tidal wave. The World Beneath served as a haven (or "ark") for the dinosaurs.

Back in Dinotopia, Marion quotes Spock to Zippo: "I am and always will be your truest friend." They prepare for the worst. Underneath, the guys have loaded the sub with sun-stones and Crabb intends to leave the brothers behind. Dad is alive and interrupts an assault, but Crabb shoots Karl in the leg and takes off. Karl had stolen Marion's sub-powering sun-stone, so when Crabb descends, he cannot get the motor going. The sub springs leaks and a sea-monster attacks.