An adaptation of Jan Brzechwa's fairy tale "Mr. Kleks Academy".

The film tells the story of the Moomin family's preparations for winter and their hibernation, interrupted by unexpected events: the appearance of the mischievous Nibling, a visit to Too-Ticky, who lives by the sea, the adventures of Little My, rescued by Moomintroll, the exploits of the Hemulen, a sports enthusiast, and so on. The story ends with the arrival of spring, the awakening of all the inhabitants of Moominvalley, and the return of Snufkin. The film is based on episodes of the television series "Moomin Stories".

Based on episodes of the series "Moomin Stories", the Moomins reminisce about the fondest moments of their lives. Moominpappa reminisces about his childhood; Moomintroll reminisces about how he, Sniff, and Snufkin set out to find out if Earth was truly threatened by a comet; and Moominmamma reminisces about the incredible visit of aliens from outer space.