The arrival of spring marks a new adventure for Moomintroll and the residents of Moomin Valley. After Snufkin's return from winter migration, the inhabitants slowly awaken from their hibernation. When the Moomins stumble upon a mysterious hat of exceptional quality, they cannot bring themselves to discard it and instead hold onto it, hoping to find its rightful owner. As Moomin plays games with his friends, he decides to hide in the silk hat but is shocked to discover that the hat has transformed him into a grotesque figure. Appalled by his unrecognizable appearance, Moomin returns to his original form after scaring those around him. Moomin and Snufkin decide to dispose of the hat by tossing it into the river. As it floats away, they contemplate who the hat might have belonged to and whether the owner will return to retrieve their lost possession.