The little boy Niels lives in the southernmost village in Sweden. He is withdrawn, doesn't like reading, and likes playing tricks on small animals. When he was playing tricks on the little fox spirit, he was turned into a thumb-sized person by the angry little fox spirit. Later, he tried to stop the goose from flying away, but failed. He is still riding on the back of the goose. So, he rode a male goose and flew with a flock of geese and started his own adventure.

Animals used to hate Niels, but the younger Niels often helped the small animals, and the animals gradually liked him again. Niels and the Goose joined the Grey Goose Team led by the Grey Goose Leader Aika, and they traveled together. Niels offended the cunning fox Smith in order to save the grey goose. Smith deliberately retaliated and almost killed Niels several times. Clever Niels asked a domestic dog for help and caught him laughing. Then Smith was sold to the zoo by the owner of the domestic dog and lived a life without freedom. The kind Niels couldn't bear it any longer and helped Smith regain his freedom.

Niels got separated from the geese because of an accident. He found that the old Diao Ge, who had saved himself, was locked in a cage in the zoo and lost his freedom. He helped Gogo escape from the cage and learned that Aika raised Gogo, but they later clashed and neither of them spoke to the other. When Gorgo helped Niels return to the geese, Niels mediated the contradiction between Gorgo and Aika, and the two animals got back together. Later, Niels learned from Aikaku that his parents were not doing well and he was eager to go home.

Niels returned home to his normal appearance, and his parents were very happy to see him. After some adventures, Niels has become a kind, brave and responsible boy. He reluctantly bid farewell to the geese led by Aika, and he will never forget that he once traveled by geese.