Nobita, believing he and Doraemon had done a good deed by saving stray cats and dogs and sending them back in time by 300 million years, discover that the usage of Doraemon's Ray of Evolution had created a cat-and-dog-person society equal to Nobita's time. When an asteroid attack is set to hit the city, Nobita and his friends must save Doraemon and ease tensions between the two sides.