A comet is speeding towards Earth - will it destroy everything and everyone?
Moomintroll decides to find out. So, with Sniff, he sets off on an expedition to ask the Professor if a comet is really on its way.
On their journey they meet some interesting people - such as Snufkin the super tramp, and the Hemulen who rescues them from an underground tunnel - and have narrow escapes from dangerous crocodiles and giant lizards.
And on their way back Moomintroll meets the beautiful Snork Maiden... But what about the comet?