The short answer is, don't bother. If you want the long answer, buckle up, kids. I have a lot to say.
The story got off to a rocky start at the introduction of the main cast. DCI Ryan is, of course, an adonis of physical perfection. His trusty sidekick DS Philips (who is, in fact, the most enjoyable character in the book) had a great deal of description. When we got to the other female police officer introduced by name, we discover that she has red hair and DS Philips would like to ask her out. But fear not, later on we also learn that she's Irish and that both Ryan and Philips agree that she "has a nice arse". No further characterisation is needed for a woman.
So my hackles were already raised when our alpha male main character met Anna, the female lead, and proceeded to be extremely rude and condescending (because no woman of 28 can possibly be a doctor and an expert in her field). But fear not, it's all okay because when she became angry at such treatment, Ryan realised how hot she was. She, naturally, was likewise smitten by his perfection and quickly forgave all deficiencies in character and manners. He continued perpetuating his alpha male instincts and despite token protests, Anna naturally quite liked being claimed as someone's own.
Of Anna we discover that she's beautiful (of course), intelligent (of course), and damaged by past trauma (of course). And that's it. That's all the character she needs, being a woman and all. Her main purpose, apart from imparting a few bits of historic lore that a simple Google search would reveal, was to be the romantic counterpart to Mr Perfect. Their whirlwind romance was trite and utterly unconvincing.
Case in point: there's a killer on the loose on Lindesfarne and Ryan is concerned for Anna's safety. So like any good knight in shining armour, he marches off to her cottage, gets no response to his knocking (what with there being music playing and all), so proceeds to knock down the door. Not simply break lock, but actually rip the door off its hinges. Hulk smashes and all that. Anna, being a sensible sort of woman and acting on instinct when someone has just removed the door off her cottage reacts like any sensible woman would: she jumps into bed with Ryan. I found it fascinating that neither the inevitable victim or the DCI thought about the killer on the loose on the island while they were going at it like rabbits in a cottage without a door. Also, FYI, the story takes place in the days leading up to Christmas, but surely being in luurve is all you need to keep yourself warm when exposed to the bracing North Sea air.
A further point that irritated me a great deal was that Ryan had suffered previous trauma and had been prescribed medication to manage anxiety and PTSD. But like any good alpha male, he refuses to take the pills and resolves to push through without therapy or any kind of help. Of course, once this trauma had been mentioned and Ryan had a few obligatory moments of staring into space, it played no role whatsoever in the story. So maybe he wasn't all that traumatised after all. In this day and age, it would be nice to see a little more realistic and sensible portrayal of mental health issues.
As for the main plot, it's unconvincing, flawed, and frankly a little boring. Even the twist at the end wasn't really a twist at all. This book fails as a crime novel as well as a steamy romance novel.
Having been annoyed by various parts of this story which seemed to belong in the group of male authors writing about depressed breasts, imagine my surprise when I discovered that L.J. Ross is, in fact, a woman. While male authors have been increasingly called out on such sexist writing as was portrayed in this novel, it made me wonder whether female authors are subjected to the same scrutiny. Or is it forgiven because the sexism is wrapped up in a cutesy romance with a HEA?
All in all, I'll reiterate my short verdict of don't bother. I'm going to further say that I'm shocked this is a best seller.