Yes this is the second in a series. Yes should read the first one before this one. But, Nesbo does an incredible job of filling in any gaps that would cause confusion if you hadn't read the first book, so you aren't lost. What is missing is the reader's relationship with the main characters. If you only read this book, I feel you would not truly understand Roy and his motivations and why he is the way he is. Reading the first book makes the reader more sympathetic and understanding on the things Roy does and why he does them. It also builds the foundation for the relationships between characters that adds to the emotions running through the second book. That being said, the first book is 560 pages and might frighten someone off. Don't let it! The read is engrossing. But, enough of that sales pitch! This book can easily be read on its own. The theme of both books is family and the responsibilities and duties to your own. Set in a small town, the theme is viewed through various families and points of view, making this either a really deep thoughtful book (if you want it to be) or a surface level small town drama suspense kind of book. I love that the reader can decide based on their own current mental capacity. 

Thanks to NetGalley and Knopf, Pantheon, Vintage, and Anchor for a copy of the book. This review is my own opinion.