I am such a Marion Todd superfan! I have been invested in this series since the first book so was delighted to be given the opportunity from the publisher to submit an early (honest, obvs) review of book 4. "What They Knew" opens on Hogmanay just before the Bells. Suffice it to say, I'll be watching Jools Holland's Hootenanny with a degree of trepidation this year.

Being reintroduced to the team is like seeing old friends. DI Clare Mackay is a stoic character so on the rare occasion we are allowed to see glimpses of her humanity, the impact is greater. This is a woman who cares deeply about the people in her life yet keeps everyone at a distance. That said, she does have romantic interests and it's nice to see this from the perspective of someone who is not a terribly young woman. This book in particular looks at the notion of staying in a relationship past its sell-by date because the alternative is loneliness. We don't see as much of Clare's family in book 4 but there is mention of James, her young nephew recently diagnosed with autism. All of these wee clues remind us that, whilst DI Mackay is ever the consummate professional, she does have a personal life which is as mundane and challenging at times as the rest of us. I love the relationship between Clare and her subordinate DS Chris West. I was pleased to see a quip about his trousers in this book and wonder whether that's going to be a running joke, as per the opening of book 2.

Now, I had a buddy reading along with me and as a result I received the following message "Is 'outside in' a Scottish thing?" Oh, how we laughed! I'm delighted that this expression has been included and that my English pal now has some new patter. As always, Todd's extensive and meticulous research shows in this book. I particularly appreciated the inclusion of the fact that "most violent crimes against women are committed by men they know". I was also fascinated to learn about the role of a Faraday cage in shoplifting!

In terms of Marion Todd's writing, the DI Mackay series is a solid police procedural. Todd has the syntax of police speak down to a tee. Her descriptions of place are so vivid the reader could be standing beside DI Mackay as she visits a potential suspect. I also love the way that Todd explains the more complicated elements of plot for the avoidance of doubt. She doesn't assume knowledge or understanding on the part of the reader and I really appreciate that, especially when there's various plot strands to pull together.

Overall "What They Knew" is another cracking read, the tension really building in the latter half of the book. I thoroughly enjoyed it and hope that Todd sustains her current rate of production because I can't get enough of the DI Mackay series.

A huge thank you to Canelo and NetGalley for an advance copy of this book which I have been eagerly awaiting, having read the previous three books in the series. I started reading it immediately and was straight back in the world of DI Clare MacKay, just like visiting an old friend. If gripping crime / police procedurals are your thing you will love this series.

A fantastic opening chapter which grabbed me immediately and the pace of the book kept my interest right to the last page.

A girl is found dead in her bath. She has light bruising on her neck but it does not look like she has been strangled. DI MacKay is called to investigate. Another body of a girl is found in a small river. Could the deaths be related? Is there a serial killer out there?

The investigation takes Clare down many avenues including an online dating app and to a possible connection with a school reunion.

Just when you think you know where the investigation is going it takes another turn to keep you on your toes!

Clare is also at a bit of a crossroads in her personal life as her fairly new partner has moved to Boston and she is considering ending their relationship. Could a dating app be her way of finding Mr Right? Or is there a possibility of a relationship with a work colleague which almost happened before she chose her current partner?

Very highly recommended and a well deserved 5 out of 5 stars.