Black Widower by Patricia Moyes

Sir Edward Ironmonger, the ambassador to the United States from the newly independent island republic of Tampica, and his beautiful, temperamental wife, Mavis, are throwing a party for the Washington diplomatic corps. despite her promises to behave, Mavis manages to insult the Isreali ambassador and is quickly removed to her room, where her corpse is discovered a few hours later. Suicide is ruled out by an autopsy, and to avoid embarassing publicity Chief Superintendent Henry Tibbett is brought in to conduct a discreet investigation.