Little Chestnut: One, two

A monstrous serial killer is on the loose in Copenhagen. Armed with only a telephone, he drives his victims to the brink of insanity. His heinous crimes bring Europol agent Mark Hess and Naia Thulin back together. Thulin had left the homicide department to take on a new job in cybercrime. The trail leads to an unsolved murder, but the real answer lies deep in the past, when an innocent school trip turned into a nightmare… It seems the evil hasn't gone away—and the worst is yet to come.