Here's a strange coincidence (at least I hope it's a coincidence...) - the bad guy in this book is nicknamed (by the Washington DC PD) as The Weasel. I have, in my to-read list, another book with the title "Pop Goes the Weasel" (Pop Goes the Weasel), wherein the apparent bad guy is the main character's step-father... nicknamed (by him, apparently) The Weasel. One book is a gritty crime novel, the other is a not-so-gritty gay romantic comedy.
As a general rule, these Alex Cross books are not mysteries - that is, Patterson doesn't try to keep us from figuring out whodunit, and often lets us (and Cross) know early on who the killer is. That's the case in this book; our killer is identified (to the reader early on, to Cross about halfway through the book) as a staff member at the British embassy. The kicker in this one is a) finding concrete evidence, and b) navigating the "diplomatic immunity" maze in order to try and convict him. And, of course, preventing him from killing again.
Our killer, Shafer, is a former intelligence operative who is playing an online game called The Four Horsemen; obviously, in the game he plays the role of Death. With the book first being published in 1999, it's interesting to read about some of the earlier uses of cell phones and the World Wide Web; Patterson, who likes to scatter pop references throughout his books, makes reference to several internet-related companies and services that don't exist anymore in 2016. But aside from these references, the books usually don't feel outdated.
One final note: As I've mentioned before, these books are generally much more gory and violent than the other Patterson books I've read. Alex Cross is an expert in mass murderers, so a lot of the killings are committed by the mentally deranged, and this definitely shows in the Cross books in general, and in this one specifically. Without giving away details from this book, it's interesting to see how Cross's family and friends react to his job, and how they are affected when the killer decides to involve himself in Cross's personal life.
So, to wrap up: another decent entry in Patterson's Alex Cross series. Definitely more violent than the average police novel. Interesting, often positive looks into Cross's personal and family life. Patterson still shows himself to be somewhat oblivious to the financial lives of police officers and teachers.