In 1993 New York City, a curious young bluebird named Buster Blaze Berdahl runs away from his siblings and encounters Rex, a bright orange Tyrannosaurus who is calmly playing golf. Rex explains that he was once a feared predator, and he begins to recount his own life story in a measured, first‑person voice.
During the distant past, in the Cretaceous Period, Rex chases a small Thescelosaurus but soon finds himself aboard a flying, time‑traveling ship piloted by Captain Neweyes Walter Cronkite. Neweyes, accompanied by his alien aide Vorb, intends to bring four dinosaurs to contemporary audiences so that children can witness real dinosaurs from the Mesozoic era. The crew aims to collect Rex, Woog, a blue Triceratops, Dweeb, a green Parasaurolophus, and Elsa, a purple Pteranodon, who together are offered a cereal called Brain Grain to grant them sentience. Neweyes promises a path to Dr. Bleeb Julia Child, who will guide them to the Museum of Natural History, and he cautions them to stay away from his unscrupulous twin brother, Professor Screweyes Kenneth Mars.
The ship drops the dinosaurs into the East River, 1993, but their arrival goes unseen by Dr. Bleeb at first. A pair of runaway children—Louie Joey Shea, a boy who fled home to join the circus, and Cecilia Yeardley Smith, a girl neglected by her wealthy parents—volunteer to help. To avoid detection, the group conceals the dinosaurs as animatronic performers for the Macy’s Thanksgiving Day Parade. The ruse nearly holds, but Rex accidentally deflates an Apatosaurus balloon during a musical number, which reveals the dinosaurs’ true nature to the crowd. The spectators cheer in awe, yet the adult crowd panic-strickenly scatters, and the four dinosaurs escape into Central Park pursued by police and the army.
Meanwhile, Louie and Cecilia meet Screweyes, who runs the horror‑themed “Eccentric Circus.” Unaware of Screweyes’s darker motives, the children sign on to perform. When Rex and the others arrive to rescue them, Screweyes deploy a sinister plan: he uses pills called Brain Drain to erase the dinosaurs’ intelligence and transform the children into mindless chimpanzees. In a grim trade, Screweyes promises to restore Louie and Cecilia to human form and to release them if the dinosaurs swallow the pills and lose their wits. The dinosaurs comply, trading their intellect for the chance to rescue the children.
That night, a kindly clown named Stubbs Martin Short, who works for Screweyes, discovers the truth behind Screweyes’s scheme and begins to question the club’s cruel methods. He warns Louie and Cecilia about the plan to exploit the dinosaurs and quietly begins to undermine Screweyes from within.
Armed with new resolve, Louie and Cecilia slip into the circus that night, where Screweyes’s tricks culminate in a drastic display of power: Screweyes hypnotizes Rex to threaten the tyrant’s own fate. A flare‑bearing crow interrupts the moment, and Rex seems poised to strike Screweyes. Yet Louie and Cecilia intervene with a heartfelt plea and a gentle, human touch, rekindling the dinosaurs’ lost sentience. The restored bond among Louie, Cecilia, and the dinos breaks Screweyes’s hold, and Cecilia confesses her love for Louie, which strengthens their resolve.
With Screweyes’s grip weakening, Captain Neweyes arrives aboard his ship to extract the children and the dinosaurs from the circus. Screweyes meets a grim fate as he is overtaken by crows, and the last crow peels away with the magical device, letting the eerie power fade. The dinosaurs and Louie and Cecilia reunite and set their next course toward a brighter future.
The journey continues as the dinosaurs reach the museum, where Dr. Bleeb awaits to guide them. The next day, the colossal show is unveiled to a crowd of eager children, fulfilling Neweyes’s original plan and allowing the public to witness the dinosaurs as sentient beings. Louie and Cecilia reconcile with their parents, and the two children form a bond, choosing to become a couple.
Back in the present, Buster returns to his family, brushing off the taunts of his siblings with a simple, warm gesture as he hugs his mother. Rex bids him good night and asks him to remember the story as he returns to his friends at the museum, a quiet reminder that wonder and memory can bridge generations. In the end, the day’s adventures leave a lasting impression on both the human world and the world of dinosaurs, suggesting a shared sense of awe that transcends time.
