The Kind Worth Saving by Peter Swanson

Private detective Henry Kimball is hired by Joan Whalen to determine if Joan's husband, Richard, is having an affair. Joan is convinced that Richard is seeing his co-worker, Pam O'Neil. Henry and Joan previously knew each other when Henry was Joan's English teacher her senior year of high school, but haven't seen each other since then. Henry begins his surveillance and finds himself befriending Pam, wondering all the while if it's a good idea. An alternating storyline in the novel concerns a teenage Joan, then a freshman in high school, on vacation with her family in Maine. There she secretly befriends a boy named Richard who lives in her hometown. Both Joan and Richard hate Richard's cousin, Duane, and taunt each other about what is would be like to get rid of him. Will they follow through with a plan to kill him? The Kind Worth Saving is a Hitchcockian puzzle, well worth a read. The book also features characters from Swanson's second novel, The Kind Worth Killing, but reading that first isn't necessary.