Based on the novel with the same name by Astrid Lindgren. Lonely little Bertil befriends the tiny Nils Karlsson-Däumling, who lives in a mouse hole under his bed and teaches him a magic spell to shrink down and share wondrous adventures in his secret world. Their idyllic fun, however, is threatened by the sinister rat Schofeline, forcing Bertil to summon all his newfound courage.