Alone in the world, Elspeth takes the position of nanny to a family on the remote Scottish island of Skelthsea.
Her charge is a strange child. Distracted and secretive, Mary hasn't uttered a word since the sudden death of her twin, William - just days after their former nanny disappeared.
Elspeth's questions are met with silence. No-one will speak of William.
Just as no-one can explain the lullabies sung in empty corridors, or the whistling that comes in the night...
With winter closing in, passage off the island turns treacherous - and Elspeth finds herself trapped.
But is this house haunted by the ghosts of the past?