Moomintroll is building a house

After the Moomintroll family has visited the Moomins, the guests leave, but they forget about her youngest and most ill-mannered sister, Little Mu. She promises to listen if they give her Moomintroll's room. And he's fed up with being kicked out of his room and decides to build a house where all the rooms are his. When Little Mu helps, everything inevitably goes wrong, but in the end, Moomintroll's building woes show him the importance of home.