After mysterious signs appear of a strange star with a tail Moomintroll and his friend Sniff set off on a journey to find out more. Their journey is packed with adventures and new friends. They discover that a fiery comet is heading towards their beloved home, Moominvalley. They don’t have much time to make their way back and warn the others about the comet.

Often regarded as the first Moomin novel in the series, as it is set in Moominvalley and introduces several of the main characters, like Snufkin and Snorkmaiden.