This Moominvalley adventure begins with Snufkin, the solitary wanderer, setting up his tent by the river, seeking harmony. Moomin, however, often feels lonely and misses Snufkin's company. The Moomin family and their friends, including Sniff and Snorkmaiden, embark on a seashell gathering trip, a joint decision Moomin initially tries to avoid. During their outing, Snorkmaiden falls into an antlion's hole while playing tag, leading to a frantic rescue effort where Sniff, despite his fear, is coaxed into helping. This incident highlights the Moomins' strong sense of community and their willingness to help each other in times of peril. A central plot point revolves around a mysterious hat, which the Moomins initially threw into the river after it caused strange transformations, like turning Moomin into a ghost-like creature and eggshells into clouds. They later discover the hat has drifted to the beach and, after retrieving it, find it transforms water into raspberry juice. This discovery sparks curiosity and a series of experiments, including Moomin and Little My secretly using the hat at night. Little My, ever the mischievous one, follows Moomin and Snufkin, demonstrating her cunning and desire to be included in all the fun. The hat's true owner is revealed to be the Hobgoblin, a creature obsessed with finding the "King Ruby" and known for riding a black panther. The hat's magical properties escalate when Moominmamma discovers a tree growing rapidly in their basement after Moomin and Little My place the hat there with a string inside. This leads to a comical and chaotic situation where the Moominhouse is overtaken by lush vegetation, much to Moominpappa's dismay, who sees it as a catastrophe. The Hobgoblin eventually appears, drawn by the hat's presence, and, after a brief misunderstanding, is revealed to be a benevolent figure. He explains his centuries-long quest for the King Ruby and, upon receiving a different ruby from Moominmamma, expresses gratitude and departs. The episode concludes with the Moomin family restoring their home, and while Moomin misses the endless raspberry juice, the Hobgoblin's hat finally disappears from Moominvalley, leaving behind a memorable tale of magic, friendship, and unexpected encounters.