A philosopher predicting disaster, black rain, and rumour of a threat from space take Moomin and his two friends Little My and Sniff on an adventure to find out what is coming their way. The trio heads toward an observatory found on the Lonely Mountains. On their way up the mountain they meet Snufkin, a wise, lonely wanderer who knows about the coming disaster: it's a comet that could hit wherever, even here. Now led by Snufkin, the expedition arrives at the observatory and learns that the calculated time is in two days. The four have two days to hurry back to Moomindale to warn everyone and to escape into a cave near the sea--and to find the sweet owner of a golden anklet Moomin found in the mountains. More and more interesting characters join the adventurers: the inventor Snork, his sister Snork Maiden, and the stamp collecting Hemulen. Not forgetting the giant octopus, the Snork-eating plant and the lizard guarding a ravine full of amethysts, the journey turns into a real adventure.
—Little My