Based on the infamous real-life 1889 Swedish murder case, the story centers on Anna Månsdotter (Gunnel Lindblom) and her son, Per Nilsson (Gösta Ekman). Following the death of her husband, Anna maintains a dangerously possessive and secret incestuous relationship with Per. To secure financial stability, Per enters an arranged marriage with Hanna Johansdotter (Christina Schollin). When Hanna moves into the farm, she discovers her husband's refusal to consummate their marriage and suspects an intimate bond between mother and son. Fearing exposure and driven by intense maternal jealousy, Anna and Per conspire to murder Hanna, leading to a grim judicial investigation.