This book was a Harry Bosch / Micky Haller combination book. Contrasting how the last Micky Haller book claimed to be a Bosch book wasn't really a Bosch book, this one is half of a Bosch book.
In particular, the narrator's perspective oscillated between third-person Bosch-is-doing-stuff to first-person here-is-Haller's-viewpoint. While initially jarring, the changing perspective worked for this book. I suspect that Connelly writes all of the Haller books in the first-person, the previous one was, so this is likely keeping in line with that style.
We see more of the dynamic between Haller and Bosch, and Haller and his ex-wife. There were a lot of mis-directions in the book, which, honestly, were a nice contrast to the normal Bosch style of he gets everything right. You know, part of the Bosch formula.
Speaking of that formula: someone dies, tunnels. The bad cop might not have done it. You'll have to read the book to be sure. I enjoyed the book enough to say it's not the first of two books in a row needed for me to stop reading a series, so I'll keep going. Bosch has to slow down at some point, right?