The narrative begins with Nobita boasting to his wealthy, arrogant friend Suneo about discovering a genuine dinosaur fossil. Cornered by his own tall tale and desperate to save face, Nobita desperately scours the city for proof. To his astonishment, he uncovers a mysterious, football-sized metallic egg in a remote quarry. Using the futuristic gadgetry of his robotic cat companion, Doraemon, Nobita incubates the artifact. To the shock of both boys, the shell cracks open to reveal a living, breathing baby Plesiosaur, which Nobita affectionately names Pisuke.As Pisuke grows rapidly, hiding him becomes an impossible and chaotic endeavor. Nobita must constantly juggle the demands of feeding an aquatic carnivore with evading his perpetually suspicious mother and
the neighborhood bullies, Gian and Suneo. Despite the mounting stress, a profound emotional bond forms between Nobita and the gentle dinosaur. Nobita is fiercely motivated by a desire to protect Pisuke from the cruel, exploitative curiosity of the modern world, realizing that a twentieth-century Japanese suburb is no place for a prehistoric creature.When the situation reaches a boiling point, Doraemon utilizes
the Time Machine to transport Pisuke back to his native Cretaceous period, accompanied by Nobita, Gian, Suneo, and Shizuka. However, a sudden, violent temporal mishap caused by mysterious black-market dinosaur poachers damages their equipment, stranding the children and scattering their return gadgets across primeval landscapes. Driven by love for Pisuke, the friends embark on a perilous, continent-spanning journey to reunite the young dinosaur with his herd.Throughout the arduous trek, the group faces terrifying hazards, including ferocious carnivorous dinosaurs, treacherous terrain, and relentless pursuit by the heavily armed poachers who seek to capture Pisuke for immense profit. Nobita is pushed to his absolute physical and psychological limits, forced to summon unprecedented courage to defend his beloved pet. The dramatic tension peaks in a breathless, high-stakes confrontation where the children utilize their wits, teamwork, and remaining gadgets to outmaneuver the ruthless criminals.Ultimately, the Time Patrol arrives, having tracked the illegal poachers through the spacetime continuum, capturing the villains and saving the children. With Pisuke finally safe among his own kind in the Cretaceous seas, a heartbroken Nobita must make the ultimate sacrifice. He says a tearful, bittersweet goodbye to his best friend, returning to the present day forever changed. The emotional core of the adventure leaves Nobita more mature, resilient, and deeply cherishing the unforgettable bond he shared with a creature from a forgotten era.