The night of the twelfth

From amazon dot com: "This psychological suspense thriller concerns the police investigation of a series of brutal torture-killings at a boys' school. The presence of an ambassador's son at the school adds the problem of political terrorism. It's a serious book about an ugly subject, but well written and shot through with Gilbert's characteristic sanity and good humor."

Set in rural England in the eary 1970s, a vastly different place than that of today.