1944 Stockholm. A brutal murder has been committed in a notorious area. One of the first to arrive at the crime scene is Elsie Swanns, a young girl who has recently joined the police service. The killer is in no hurry to escape from law enforcement, and when Elsie gets in his way, her fate is already sealed... Thirty years later, Britt-Marie Udin, one of the first female detectives in Sweden, begins investigating a complicated case. The crime scene makes her shiver: everything is too reminiscent of the nightmare of her past: many years ago, in these slums, popularly nicknamed the Swamp, her mother died. The criminal remained true to his style in everything. Only this time, the victim survived. Britt-Marie is not taken seriously by her colleagues, but she is a force to be reckoned with, and it seems that she is about to get closer to the solution. However, her persistence is not enough to fight the ruthless killer. The criminal escapes, and Britt-Marie disappears with him. In the 80s, her mysterious disappearance begins to raise questions. It seems that the so-called Swamp Killer has made his presence known again. Another murder after so many years. The police turn to Hannah, a profiler, hoping that she will help track down the criminal. But everything is to no avail, the killer is elusive. And now it’s 2019. Malin Brundin takes up the case, she believes that she will be able to stop the Swamp Killer, who has eluded justice for so many years. After all, for so many years, women who have won their place in a world that completely belongs to men have been hunting the shadow alone. Will the killer escape again?