Cnut - They Tumble Headlong

Follow the money. Cnut, his own life in imminent danger, comes close to falling over the body of Eli Peterssen, strangled with a bicycle chain - a unique weapon, as far as he is concerned, and starts the investigation process into her murder. Motives, in her case, are not difficult to identify. Eli, he finds, was something else: a seriously rich nymphomaniac, who filmed herself in intimate action with many men, possibly for blackmail purposes; a talented major financial crimes investigator, who has ruined a whole bunch of businessmen, and caused one to commit suicide; and the avowed target of more than a dozen threatening letter writers.
Suspects abound, the main one Max Aasgard - her most recent lover, and the latest businessman she intended to destroy, seeking evidence not only from him, but also from his senior employees, while bedding them too. When Max's ex-chief accountant is killed in exactly the same way as Eli Peterssen, Cnut, Ilse, and the team, up to their elbows in evidence, realise that they are faced with a serial killer, and there is no clear motive.
As the bodies pile up, and the possible motives change yet again, Max is always there at the centre of things, though Cnut is sure that the entrepreneur is not the killer. Things come to a climax when the detectives find themselves under fire, when going to arrest the likely murderer, and that arrest, to say the least, does not go according to plan. The twist in the tail is ironic in the extreme.