Night and Day by Robert B. Parker

Things are getting strange in Paradise, Massachusetts. Police Chief Jesse Stone is called to the junior high school when reports of lewd conduct by the school's principal, Betsy Ingersoll, filter into the station. Ingersoll claims she was protecting the propriety of her students when she inspected each girl's undergarments in the locker room. Jesse would like nothing more than to see Ingersoll punished, but her high-powered attorney husband stands in the way.