Lasi and the castle mystery

A stoat, brown in the summer and white in the winter, lives happily in its burrow. One day, it sees a boy fleeing along a path, who is soon taken away to the castle dungeon. Before being captured, however, he manages to tell the stoat what happened, and she decides to free Jan with her friend, the she-bear. In the end, all three of them are imprisoned. A passing ghost offers to rescue them, but... Duchvost the ghost is a total muddlehead!