Far up in the north is a blueberry-blue house with a grass roof, where Lisa and Nils live. One day a tourist arrives: Otto has cycled for months, maybe years, to visit his friends. Otto wants to do a spectacular painting of the northern lights to remember his visit, but he is from a hot country and it is very cold here. He can't paint for shivering so hard. His friends decide to knit him a sweater.