Astrid Lindgren's detective story is about Bill Bergson, a more-or-less ordinary Swedish boy with an extraordinary fascination for detective work. He lives in the city Lillköping. He identifies clues, investigates enigmas, and solves the riddle surrounding a mysterious stranger while the police and other adults overlook or dismiss the whole matter. He and his friends several times solve real crimes including murder and kidnapping. Lindgren wrote shorthand for Harry Söderman, a doctor in Criminology and it was during this work that she learned the basics of criminology that she later used in her stories.