Svante is a young boy who lives with his family in a Stockholm apartment. One day he meets Karlsson, a chubby little man in the prime of his life, who can fly using a propeller on his back and who lives in his little house on the roof.
Karlsson-on-the-Roof is a character who features in a series of children's books by the Swedish author Astrid Lindgren. Lindgren may have borrowed the idea for the series from a similar story about Mr. O'Malley in the comic strip Barnaby (1942) by Crockett Johnson.