When the body of a young girl is found hanging from a tree, the only clue the police have is an airline tag around her neck. It reads 'I'm travelling alone'.

In response, police investigator Holger Munch is immediately charged with assembling a special homicide unit. But to complete the team, he must track down his former partner, Mia Krüger - a brilliant but troubled detective - who has retreated to a solitary island with plans to kill herself. Reviewing the file, Mia finds something new - a thin line carved into the dead girl's fingernail: the number 1.

She knows that this is only the beginning. To save other children from the same fate, she must find a way to cast aside her own demons and stop this murderer from becoming a serial killer.