After spending six months unsuccessfully trying to find 17-year-old Julie Vinding (Alvilda Lyneborg Lassen), who went missing on her way home from a party in a Copenhagen suburb, detective Jan Michelson (Kenneth M. Christensen) is taken off the case by his superiors who believe the girl is dead.
[3] Michelson's boss MT (Peter Mygind) brings in criminal profiler Louise Bergstein (Natalie Madueño) to assist in the investigation.
[6][7] Bergstein soon finds similarities to unsolved murders of two other young men on the island, Kasper Larsen (Téo Lepetit) and Ricky Hansen (Peter Zandersen), which also occurred five years earlier.
[6][8] When a fifth young man, William Fjeldby (Oscar Dyekjær Giese), a friend of Markus Ejbye, is murdered in similar circumstances, she teams up with Karina Hørup (Helle Fagralid), the lead detective on the cases, to track down a serial killer who has resumed killing after a five-year hiatus.
[18][19] Arte broadcast season 1 in September 2020 as Le Tueur de l'Ombre in France and Darkness – Schatten der Vergangenheit in Germany.