When Moominmamma is accused of an unlikely crime, Moomintroll turns detective to try to save her. Can he succeed where his father couldn't.

Moomintroll and his friends find a magical and mysterious hat. While fun to begin with, they soon realise that the hat is dangerous.

In his desire for more independence, Moomintroll pushes Moominmamma away. But he soon becomes jealous when she finds a new outlet for her motherly love.