Coup de Grace [first edition]

Newly minted PhD and sometime amateur detective Sarah Deane goes to teach at a New England girls' boarding school with a famously iron-fisted French teacher, Mme. Carpentier. But soon afterwards an art teacher turns up dead, bludgeoned to death on a campus path. Was it a case of mistaken identity, with the killer really out to get Mme. Carpentier? No one can stop Sarah from investigating....