Moomintroll, Sniff and Little My set out to stop a comet approaching the Moominvalley. Along the way they meet Snufkin, the beautiful Snorkmaiden, Snork and Hemulen, who join them in their quest.

A young boy named Guskou lives in the countryside with his parents and little sister. A string of droughts and other natural disasters tear the family apart, and Guskou is forced to leave home and seek his fortunes on his own. Driven by a desire to improve the quality of life of his poor countrymen, he eventually joins a group of scientists called the Ihatov Volcano Department; he takes part in scientific projects to fight the natural disasters that drove him from his home.