This book is interesting and the mystery is unusual. However, the story would probably appeal more to readers familiar with the series due to the fact that so much of the drama involves events and people who appear in prior books. I am not sure that new readers will be properly invested in the numerous events that are extraneous, or only strenuously connected, to the primary mystery. Indeed, one of the primary mysteries involves the murder of a person who was pivotal in two earlier books and the fallout of that murder affects the main characters personally based on, in part, emotional and traumatic events that occurred in earlier novels. So much that happens in this book involves facts, characters, and events that appear and are fully explained before Hot Lava even starts. I personally started reading this series in the middle and was very disappointed in the book that I read first (Shattered Palms) due to how much of that story was based on important past history that was not adequately explained.
However, for readers of the series, the events pack a powerful punch. Indeed, the first crime presented in the book seems a little underwhelming given all of the turmoil occurring in Lei and Michael's lives. That turmoil is what grabs readers' emotions and real interest in my opinion.
I did have a few criticisms, mainly related to continuity issues. I can't describe many of the problems since it would reveal spoilers, but one example relates to whether a character was murdered given the lack of needle marks on her body, but that character was on a morphine drip so injecting a poison or an overdose could have easily been accomplished by injecting it into the IV tubing. In addition, some events and thoughts feel superficially facile. None of these detract substantially from the main action, but they create irritating little jabs to the story.
Overall, I recommend this book to fans of the series.