I will admit that jumping into the middle of a multi-novel series doesn’t always yield the best results. While authors aim to write each book in such a way that anyone can drop in at any time and still get the gist of things (and this book is no different), I feel that there is a richness to the characters that is lacking by not having the full background.
Overall, I liked this book, but I did find it slow in parts. The middle of the book is where authors tend to not be able to hold my attention, as was the case here. The story line was quite complex, with multiple mysteries at once and the interleaving of many relationships, so it became mired in a too much detail in some spots. I suspect a broader brush could have been used to fill in the investigations and kept a faster pace. The problem may well have been that there were too many mysteries happening in one book to really be effective in the storytelling of all of them.
I would consider going back and reading earlier books in the series to learn more about the main characters. I would definitely recommend starting at the top with this one.