Joachim Kroll kills for more than twenty years across northern Germany before police catch him in 1976, and by then he has confessed to roughly thirty murders, most of them women he strangled after finding them walking alone in rural areas around Duisburg. The film traces how his violence escalates over time, from assault and strangulation to acts of dismemberment, and how his compulsions eventually turn toward children, including the murder of a four-year-old neighbor whose remains he partially consumes. Investigators and commentators walk through the case timeline, including an earlier, chilling detail: Kroll cooking and eating a cat, a step his own accounts frame as a rehearsal for what came next. The documentary uses interviews and expert analysis to lay out how a man neighbors considered unremarkable evaded capture for so long, and what his eventual confession revealed about the scale of his crimes. It stays close to the police case file and victim details rather than speculation, presenting Kroll as one of postwar Germany's most prolific and long-undetected killers.