The Silence of Herondale — Joan Aiken

Deborah Lindsay sought peace and security when she accepted the post of governess to a teenage girl. Instead she found terror and murder.

Isolated in the Gilmartin ancestral home in Herondale, Deborah and young Carreen were left to face a nameless, unseen danger lurking in the frozen village, where only the flick of a curtain at a window or some random footprints in the snow, showed that it was inhabited at all.

Alone in a house that had known violence, Deborah turned to Carreen's cousin Jeremy, as attractive as he was cynical and mysterious. But was he really a friend, or was he the enemy? In spite of Jeremy -- or because of him? -- Deborah found herself fighting for her life in an affair so bizarre as to shatter the silence of Herondale forever.