The fourth book in the series about Yesper and Noper deals with the unfamiliar. One day, Yesper and Noper see that they have a new neighbour. Yesper is happy, while Noper is extremely sceptical, building a tall fence to stop their neighbour coming to see them. Yesper builds a bridge precisely to enable the neighbours to visit each other. Hasn’t Yesper heard that you’re not supposed to talk to strangers? When their neighbour suddenly closes the curtains, Noper thinks this is clear proof: the neighbour has something to hide!