When a young boy discovers the body of a woman beneath a thick sheet of ice in a South London park, Detective Erika Foster is called in to lead the murder investigation. The victim, a beautiful young socialite, appeared to have the perfect life. Yet when Erika begins to dig deeper, she starts to connect the dots between the murder and the killings of three prostitutes, all found strangled, hands bound, and dumped in water around London.

When a boy leaps to his death from a bridge in the northern town of Umeå, Sweden, police discover drugs scattered in the snow near his body. The town has seen a dramatic increase in narcotic use among its youth, but nobody knows where the pills are coming from.

Fresh from maternity leave, Detective Elma finds herself confronted with a complex case, when a man is found murdered in a holiday cottage in the depths of the Icelandic countryside - the victim of a frenzied knife attack, with a shocking message scrawled on the wall above him.

When Óttar Karlsson, a wealthy and respected government official and businessman, is found murdered, after failing to turn up at his own surprise birthday party, the police are at a loss. It isn't until young police officer Sigurdís finds a well-hidden safe in his impersonal luxury apartment that clues start emerging. As Óttar's shady business dealings become clear, a second unexpected line of enquiry emerges, when Sigurdís finds a US phone number in the safe, along with papers showing regular money transfers to an American account.

Bergen Private Investigator Varg Veum is perplexed when two wildly different cases cross his desk at the same time. A lawyer, anxious to protect her privacy, asks Varg to find her sister, who has disappeared with her husband, seemingly without trace, while a ship carrying unknown cargo is heading towards the Norwegian coast, and the authorities need answers. Varg immerses himself in the investigations, and it becomes clear that the two cases are linked, and have unsettling - and increasingly uncanny - similarities to events that took place 36 years earlier.