I do not have to give away the solution to the mystery to tell you that, in fact, Zander Zahn is a murderer. We find out early on in this book that Zander murdered his mother when he was a child. However, since it was determined that he was in a disassociative state at the time, he was not prosecuted. In addition to this mental disorder, he is a hoarder (but hoards in a particularly organized way), has periods of mania, obsessively fears germs and touching other people, and is just difficult to talk to. But, he is such a brilliant mathematician (or so we are told, without any details) that the university says they are "lucky to have him in any capacity", even though he is so "socially challenged" that he cannot even teach a class.

I can think of two reasons that a person like this might wind up as a professional mathematician. Firstly, he probably would be drawn to the orderliness of mathematics as opposed to most other human endeavors. Moreover, even though mathematics is more of a social activity than most people think, success in mathematics probably depends more on the quality of one's work and less on extraneous personal factors than most other professions. So, I cannot say that this is particularly unrealistic (aside from the oddity of the particular constellation of symptoms described above). Nonetheless, I do worry that as it becomes a stereotype it will lead people to falsely assume that most (or even many) mathematicians are like this, or to assume that anyone who has symptoms like these must be a genius. These concerns are only somewhat addressed by the fact that Zahn does have an assistant, who "has advanced degrees in physics and mathematics from USC", dresses like "a Miami Vice drug lord" and is "undoubtedly as socially smooth as his mentor was socially awkward".

In the only scene where math is discussed explicitly, FBI agent Vince Leone tries to use a mathematical metaphor to convince Zahn to talk to them about what he knows:

I do not think the author knows much of anything about mathematics. Aside from the discussion above, there is also a remark later in the book, when the investigators are looking through Zahn's belongings for clues, that a row of file cabinets "that had to be fourteen feet long and five feet high held nothing but math papers. It looked like every math paper Zahn had ever completed in his life". I do not think any mathematician has produced that many papers. I am not an especially prolific mathematician (you can see a list of my papers here), but I am not far at the other extreme either, and my papers fill just a single drawer. I think, perhaps, Hoag simply does not really mean "math paper" (a research paper published in a refereed journal); perhaps she has in mind every homework problem he did as a student or assigned as a professor? Or does she mean papers that he read rather than wrote?

As a mystery and as literature, I'm afraid I cannot say I thought this one was particularly good. From my perspective, it only excels as an example of the way that the stereotype of the insane mathematician is useful to authors. The reader immediately knows what to expect from this character: loss of touch with reality, lack of concern about people, brilliant logic interspersed with moments of utter insanity, etc. A perfect suspect for a mystery novel like this.