It is only the beginning of May, but in Oslo a brutal heat wave has coincided with an alarming increase in violent crime. In the latest instance, police investigator Hanne Wilhelmsen is sent to a macabre crime scene on the outskirts of town. An abandoned shed is covered in blood. On one wall an eight-digit number is written in blood. There is no body or any sign of a victim. Is it a kid's prank or foul play? Is it even human blood?