Jules, a volunteer for a nighttime helpline assisting women traveling alone, receives a distressing call from Klara, a young mother. She claims that a serial killer, dubbed the "Calendar Killer," has given her an ultimatum: kill her abusive husband, Martin, or be murdered herself. The killer's signature involves leaving the date of each intended victim's death written in blood.
As the night progresses, Klara recounts her harrowing experiences of abuse and manipulation by Martin, a high-ranking government official. Jules becomes her lifeline, guiding her through a desperate attempt to survive.