Moomintroll and Sniff set sail towards the Lonely Mountains, and on the way they meet Snufkin, who joins them. The river takes them into a cave under the mountains where they almost fall into a hole, but at the last moment a Hemulen inadvertently rescues them when he mistakes Snufkin's harmonica-playing for a rare caterpillar and reaches his butterfly net into the cave to catch it. They find themselves in the Lonely Mountains and set off towards the Observatory. On the way they are attacked by an eagle and Moomintroll finds a gold ring, which Snufkin tells him belongs to the Snork Maiden he had met a few months earlier.