Before the events of the film, Moomin's father had finished building Moominhouse. During one rainy evening, the Muskrat suddenly appears at the front door to stay because his riverbank home had been destroyed by Moominpappa's bridge, built earlier that day. The next day, the rain's turned everything black and according to Muskrat, it is soot from outer space. He believes that a threat is coming from space and nothing can be done. Moominpappa gets an idea about the astronomical observatory in the Lonely Mountains, where a telescope can see far into space. The next morning, on their way, the trio meets Snufkin for the first time, who has heard about a comet that could crash to Earth at any time. He joins the group, and they climb the steep mountains towards the observatory. On the way, Moomin finds a golden anklet, which Snufkin knows belongs to the Snorkmaiden.