Undercurrent — Bill Pronzini

Three months of marriage to Walter Paige had been enough to send Judith Paige to the Nameless Detective, suspecting that her husband's weekend "business" trips mask an affair. The detective follows him to a coastal village called Cypress Bay and watches his motel room. Although he sees no one go in, soon he finds Paige inside, the victim of multiple stab wounds.

Searching an elusive but omnipresent balding man who Paige had met earlier, and following the lead of an old paperback mystery found in the motel room, the detective becomes aware of frightening tensions in the village, undercurrents that surface in two more brutal deaths before the startling final discoveries are made.