Moreover, "leopard" refers to the stealthy tread of the killer in the book, while "armoured heart" is what Harry Hole himself gains by his experiences.

Kaja Solness, a new Norwegian Crime Squad officer, tracks down Hole and asks for his help investigating possible serial killings in Oslo.

Upon his return, Hole finds that Crime Squad is in the middle of a power struggle with Kripos and its power-hungry head, Mikael Bellman, who seeks to put his agency in sole charge of the country's murder cases.

Hole is reluctant to take part in the investigation until a female MP, Marit Olsen, is found murdered in a park.

Suspicion initially falls on a man known to have been at the ski lodge at the time, Elías Skog, but he is eliminated from the enquiry when he is murdered by the killer.

After Hole forces Bellman to include him on the Kripos team, he finds that another person had been at the ski lodge at the time of the first three murders, Iska Peller.

Hole manages to escape and, following clues given by one of the associates, finally confronts and kills the culprit at the lip of a live volcano.

It is tacitly suggested that Hole helps the Snowman to commit suicide out of remorse for having failed to follow his father's request for him to perform euthanasia.