The monsters need the help of the children to find their way back to their world. So, siblings Maikki and Hilla decide to accompany Grah and safely bring their new friend home. They are supported by an old door guardian and Maikki's talking bathrobe. While the two girls face several adventures underground, their brother Kaapo comes up with a clever idea on how he can help his sisters from home: whatever he puts in the pocket of his bathrobe reappears underground in the talking bathrobe! And so, not only sandwiches find their way into the fantastic world of the monsters.