As spring blooms in Moomin Valley, Moomintroll and friends prepare for a new adventure. Snufkin's return marks the end of hibernation, coinciding with the discovery of a mysterious hat that triggers a curious chain of events. After a playful mishap with the hat transforms Moomin into a frightening being, he grapples with his altered appearance. Reverting to his true self, Moomin and Snufkin bid farewell to the enigmatic hat, pondering its origins and the possibility of its owner's return.