Former LAPD detective Peter Decker and his wife Rina have moved to upstate New York where Decker now works for the small Greensbury Police Department. As the book opens, Tyler McAdams - who briefly partnered with Decker at the Greensbury PD before starting Harvard Law School - asks to stay with the Deckers to study for finals. Before McAdams can crack a book the body of Eli Wolf, a student from local Kneed Loft College, is found in the woods - and the Decker/McAdams partnership is (temporarily) back on.
While investigating Eli's death, which appears to be a suicide, the detectives learn that Eli is a math genius who comes from a Mennonite family. Faculty and fellow students at Kneed Loft explain that Eli was studying an esoteric field of mathematics involving Fourrier Analyis, Fourrier Transforms, Eigenvalues, and Eigenvectors which - in short - can be used to make money in the real world. One application, for instance, is used to predict changes in the stock market. So it's no surprise that - when some of Eli's research papers turn up - lots of people are anxious to get their hands on them.
As the story unfolds the detectives talk to a number of people in Eli's orbit including his mother and father; his thesis advisor; professors on his thesis committee; other faculty members; the dean of student life; the RA in his dorm; fellow math majors; and so on. One attractive math student, Mallon Euler, seems especially interested in Eli's papers and takes to stalking/flirting with Detective McAdams in an obvious attempt to get a look at them.
Before long the body of another victim, a math professor, is found in the woods - and this time it looks like murder! Who knew advanced math could be so dangerous?
The investigation proceeds rather languidly as one or both detectives (and sometimes Rina) drive here and there to visit Eli's family, get help from a Harvard math professor, speak to the brother of a victim in New York City, and interview local persons of interest. The detectives also get relevant phone records, examine victims' computers, collect text messages, etc. A sketchy monetary scheme is uncovered, as well as an illicit affair, faculty rivalries, professional jealousy, misogyny, and other shady behavior.
Step by step Decker puts together all the clues and learns the identity of the murderer.
For me this is just an okay addition to the series. The mystery is mildly engaging and the (brief) explanation of the fancy math is interesting, but the story meanders along with minimal excitement. Also, it disturbed me that Rina tags along on police interviews. What cop would take his civilian wife along during an investigation? This has to be against the rules... besides being potentially dangerous (McAdams was already shot in a previous book). It feels like this plot device was used just to give Rina a role in the story - which seems to be to provide tasty kosher snacks, schmooze with the Mennonite mom, and throw out a suggestion every now and then.
Fans of the series might enjoy the book just to see what some favorite characters are up to - but very few ancillary characters from previous books make an appearance. To me it feels like the Decker series needs a jolt of electricity.