Along side the very well thought out plot mechanics Gerard O'Donovan makes a number of very smart choices in the book, all of which pay off. The first is that Mike Mulcahy has no serious personality defect nor any dominant flaw that both drives him and is the source of his effectiveness at his job. He is a committed, professional police officer who works really hard with his team to push forward with his investigation. While he does stretch his bureaucratic constraints to a satisfying maximum he does so for an entirely credible reason. Also his boss is competent, generally supportive and smart, pretty much what someone who becomes a senior professional officer would probably be.
Siobhan Fallon is a very well realised recovering victim of an enormous trauma who is trying to restore her life and finds that work is the best way to that. It gives her investigation a personal edge and urgency which allows her to pursue the story past the point where it has become dangerous and not seem to be driven by plot requirements. Her search for a missing woman is a search for her missing self, made clear with a light touch that gives a necessary urgency without poking the reader in the eye.
Gerard O'Donovan uses the plot a chance to have a sharp look at the greed that tumbled Ireland in political and economic austerity, the clever knot at the heart of the book is woven from huge, criminal greed, the lesser versions also get a look in. This sharply realised context provides a great platform for the action. Top notch crime fiction.