The first children's novel by Guido Kasmann tells the story of the self-confident Kathi, who meets the little ghost Gregor von Gutenbrink from the house of Niederfahrenhorst on the ghost train at the Kummerschreck fair. Kathi has just fallen in love and has to write a math test for which she has practiced shockingly little. Then the ghost Gregor intervenes, who knows nothing about being in love but can imitate voices. Together, the two experience many exciting and funny adventures.