Black Lake (Svartsjön) is a 2016 Scandinavian TV series. Originally released in Sweden and Denmark in October 2016, it is a co-production of TV3 Sverige, TV3 Danmark, TV3 Norge, Viaplay, and Jarowskij.
The eight 45-minute episodes were shown weekly on BBC Four from 16 September to 7 October 2017, with two episodes back-to-back each week.
Johan takes his brother and six friends to the north of Sweden because he is thinking of purchasing a disused ski centre close to the border with Norway. It never officially opened because a family of four was murdered in the hotel's cellar shortly before it was due to open 20 years ago. Johan's girlfriend, Hanne, who has spent years recovering from the guilt of letting her younger brother die in a boating accident quickly comes to believe the building to be possessed by the spirit of a dead child (a myling). At the same time the unpleasant caretaker, Erkki, is trying to scare them away from the property, with assistance of two Norwegian brothers who run a nearby snowmobile business. Despite accepting Johan's proposal to marry, Hanne becomes attracted to Jostein, the younger Norwegian brother.
Hanne notices that a series of child's drawing she found in one of the hotels start to become reality. She also discovers that "kill or be killed" are the meaning of the Sami words written on paper and walls around the hotel. The group hold a seance, Hanne believes the ghost of a young boy named Mikkel is trying to contact them. Jessan, one of the party gets a red-eye, and starts to behave strangely. Hanne speaks to the detective who investigated the first murders. He tells her that he thought Helgesen, the resort's previous owner, was not convinced he had done the killings despite confessing to the crime. When Jessan tries to kill her boyfriend, Frank, she is subdued and tied up. Hanne discovers from talking to her that she has been having nightmares. Jessan then reveals her binds have become free and hides in the toilet. When the police breakdown the door, Jessan is found dead in a frozen scream.
Osvald, who is dating Johan's brother, gets a red eye and disappears in the cellar. Hanne finds the cellar door open and goes into investigate where she is attacked and has to flee from a mysterious attacker. While in the cellar, she finds a secret room that contains medical files. The hotel was previously a sanatorium before being converted into a resort. Hanne, her sister Mette, and Frank decide to leave. But Hanne grabs the car's wheel causing the vehicle to crash when she sees a child in the road. Lippi seriously injures himself after finding the body of Osvald in the cellar. Mette, who is a doctor, returns just in time to save Lippi. Meanwhile Elin, an old flame of Johan's, has got a red eye and starts to walk around in a trance. Terrified by the notion "kill or be killed", she strangled the severely injured Lippi. Later Johan finds her bracelet and realises she killed his brother. He strangles her to death.
Mette discovers why Erkki has been so unpleasant since their arrival. He has allowed Dag and his brother Jostein to use part of the cellar as a cannabis farm. Johan and Frank confront the brothers but Dag stabs Johan and slits the throat of Frank. When he goes to kill Hanne, Jostein shot him dead. She leaves walks into the mountain and communes with her dead brother, Jacob. They conduct another seance. this time Hanne is attacked by something and gets a red eye. All three go to Erkki's house. Despite being armed and uncooperative, he explains that he and his brother Mikkel lived with their doctor father at the sanatorium. Erkki said his mother was a Sami who had a relationship with his father. But because he believed in Aryan superiority he saw Erkki as an inferior race. After Erkki beat his brother in a fight, his angry father strangled Mikkel for being weak.
After returning to the hotel, Hanne notices that one of the child drawings shows the bed in the cellar's secret room with a space underneath. Climbing under the floor, Hanne recovered Mikkel the brother of Erkki. But before they can give the body respectful funeral rites, Erkki stops them. Johan, who now has the red eye, returns because he was not fatally wounded by Dag's knife due to a phone, and shoots Erkki. However, outside the cellar Hanne kills Johan when he attempts to kill Jostein. The three then burn the body of Mikkel on a traditional funerary pyre. They then pack their things and leave. However, on the drive back to civilisation Jostein removes his sunglasses revealing he now has the red eye.