We had a body, a crime scene and an indisputable murder, but not only did we not have a motive, a weapon or a suspect, we had no idea how the murderer could possibly have fled the victim’s flat after firing the fatal shot.
-- K2 (Day One, I paragraph 4)

Importance: Detective Inspector Kolbein “K2” Kristiansen responds to a murder called in by Constable Asbjorn Eriksen. As K2 learns, there clearly has been a murder, but how Harald Olesen has been killed, why, and how the killer has managed to escape are entirely unknown. A classic locked-room mystery has been set up by the author, which K2 must now proceed to solve.

The most pressing question therefore was, how had the murderer managed to leave the flat in those few seconds between the shot being heard and the neighbors arriving at the scene?
-- K2 (Day One, II paragraph 5)

Importance: K2 probes the locked room mystery that has now unfolded surrounding Harald Olesen...