Think of a Number, by John Verdon, A-minus, narrated by George Newbern, produced by Random House Audio, downloaded from audible.com.

Dave Gurney has just retired from the NYPD after 25 years. Because his wife, Madeline, wanted to live in the country, they moved to upper state New York. While Madeline is happy with her gardening and her clubs and her more serene life, Dave finds he is getting bored. When someone he knew in college calls him up seeming really scared, and pretending a strong friendship they never had in college, he was curious enough to meet him. Mark was receiving taunting letters. In the first one he was told to think of a number. Then when he opened the separate envelope that came with the letter, the number printed there was the same one he had thought of. Seemingly the letter writer knew him better than he knew himself. Mark became more and more frightened as the letters continued and became more threatening. Dave finally began to pay attention too, especially after Mark was killed. And as Dave investigates further, he finds himself in the middle of the plot of a serial murderer, and Dave himself comes into his sites. He is forced to concede that the way he lived his life, hiding all feelings, was leading to very dangerous risk taking which now could involve putting Madeline in danger as well. This is a debut novel and very very good.