Mette Oda Lise Luise Inger is ten years old and is simply called Molli by everyone. She doesn't like to sleep with the bedroom door closed or jump off the swing. But she can turn a hand mixer into an electric toothbrush because she is a great inventor! However, no one at home notices this because everything revolves around her tiny baby brother. Additionally, Mom's strange new boyfriend has just moved in with them. Luckily, Molli can always run over to her best friend Gro! The two actually know everything about each other - but Molli has a secret. And when they discover a strange mailbox in the birch grove containing a postcard, the secret becomes much bigger...