A young woman is playing the piano at a wild party. When asked to play a special tune, she begins but stops abruptly and rushes out, visibly upset. Alone she starts to walk home through late night central Stockholm. Crossing a bridge, she has a conversation with a drunk artist, and after his persuasion, out of kindness, she gives him money for the sketch, but does not take it. Arriving at her apartment, she straps a rope to the ceiling and hangs herself. The next morning her body is found by a housekeeper.
The police arrives and ask questions to her neighbours. The young woman's name was Dagmar Brink, and she was something of a loner. Nobody knew much about her, although she had lived for a while in the building, but everyone states that she seemed like a sweet and nice girl. Her closest neighbours in the flat next door, writer Anders Wikner and his wife Britt, are both shocked by the girl's suicide. Soon Anders starts to investigate what happened. He contacts the few people who knew her and asks them questions. He meets artist Elias Körner who painted a portrait of her, an old bank manager who had a cold meeting with her, a woman who shared a room with her once, an ex-husband, and the singer whose party she attended the night of the suicide. Anders' wife also turns out to have a story about Dagmar and what happened one night in Dagmar's apartment. The different people's meetings with Dagmar are told in several flashbacks.
