The story begins a few weeks after the events of "The Moomins and the Great Flood", as the Moomin family are settling into their new life in Moominvalley. Sniff, who is now living with the Moomins, discovers a mysterious path in a nearby forest. As he and Moomintroll explore it, they meet the mischievous Silk Monkey and arrive at a beach, where Moomintroll goes pearl-fishing. Meanwhile, Sniff and the Silk Monkey find a cave, and the three decide to hide Moomintroll's pearls there.