During a playful afternoon by the river, Nobita stumbled upon a drowning stray dog. Moved by pity, he brought the canine, whom he christened Ichi based on the Japanese onomatopoeia for a dog's bark, back home with him. He hid Ichi inside a makeshift kennel on his wall and secretly nurtured and entertained the pup with his Kendama, a traditional Japanese toy. Later, he rescued a wet and bedraggled kitten whom he named Zubu. Nobita went on to take in more abandoned and hungry cats and dogs. Overwhelmed by the growing menagerie, Nobita and his friends devised a plan to send the animals 300 million years back in time. Before their departure, they equipped the pets with a food-making machine and used the Ray of Evolution to enhance their survival skills. The group vowed to come back to them later. Their anticipation turned to alarm when, upon returning, they landed 1,000 years earlier than planned. They chanced upon an unexpected discovery: the dogs and cats had undergone a drastic evolution and built a sophisticated society. The broken-down time machine left them stranded in a prehistoric time, and their only chance of returning to the present was to repair the machine. Unfortunately, the group also learned that Earth was about to collide with a cluster of asteroids. Would Nobita be able to fulfill his promise of reuniting with Ichi? And what about Hachi, who bore an uncanny resemblance to Ichi? The 300-million-year odyssey of time and space would soon unfold.