When all the people of the forest started making the same secret sign - a star with a tail on it - Moomintroll, who was a thoughtful fellow, recognized it as a warning. So he and Sniff, the small animal, set out for the Observatory on the Lonely Mountainsto ask the Professorif a comet was really on its way to destroy the Earth. And on their way they met some interesting people, and had some narrow escapes . . .