After Suneo bragged about having a ranch, Nobita was asked whether or not he has one, pressuring him to say yes. Doraemon won a number of lotteries for useless planets in the belt between Mars and Jupiter. When Suneo and the rest came to see the ranch, Nobita happened to read the last of the lottery number to the go-anywhere-door, leading them to a huge dreamlike area. As Nobita's toy horse pranced around because of the wind-up life gadget, Suneo and the others became interested in doing the same to their toys and let them live in the area. So they decided to make their own clockwork city.

After bragging about receiving a space trip ticket from his father, Suneo concedes they would have to wait quite a while until they can actually go. So, Nobita and co. turns to Doraemon for it, but they were given a space simulation game to play together instead. Unfortunately an accident with another gadget occurred, leaving Suneo and Giant trapped inside the game, only to be picked up by someone from outer space. Nobita, Shizuka and Doraemon then pursued the UFO that has the game inside it which took them all to a real space adventure.

Nobita and his friends gathered at Shizuka's house when they heard about the news about missing flocks of bird species. Nobita believed they were taken away by winged creatures and became obsessed on flying on his own. He created mechanical wings and upon the experiment he encountered an actual winged creature flying out of a time-space distortion. Upon helping him whose name is Gusuke, Nobita and his friends were sucked into the distortion and reached Gusuke's home, Birdpia or the world where the winged creatures live.

One day, Nobita finds a stray dog drowning in a river while playing by the river side. Feeling sorry for the dog, he decides to take it home by hiding it in a "kennel on the wall" and names it Ichi (originated from "One", which sounds similar to "wan", the sound a dog makes according to the Japanese language), and secretly feeds it and plays with Ichi with his Kendama to find. Soon after, he also adopts a stray cat named Zubu (or wet in Japanese, due to the discovery of it in a rainstorm)... and many other stray cats and dogs. With so many stray cats and dogs, Nobita, along with his friends, decide to send them back in time, 300 million years ago, where there was no other living beings around. After using the Ray of Evolution to allow them to operate a food-making machine, they depart, with a promise to return to the present. However, when they try to visit them the next day (from their point of view), they encountered a time-space anomaly, sending them crash landing 1,000 years before their original time-destination— to their surprise, They found out the dogs and cats have evolved enough to form a civilized society that rivaled those of Future Society. As the time machine is broken, they try to find help to repair it so they can continue their chrono-journey, only to learn of a bigger issue — a cluster of asteroids are going to Collide with Earth. Will Nobita finally reunite with Ichi, as he promised? More over, what's with Hachi, a dog who resembles Ichi greatly? The 300 million years of time and space adventure begins.