There is something rather disquieting about Sallie Declan, a young American in London, and it is not just her obsession with Henry James's The Turn of the Screw, the subject of her PhD thesis.
There is her decision, almost casually taken, to leave her studies for a temporary job as a nanny in a large country house.
She seems to display astonishing naivety as she build a fantasy about her emotional future there.
Surely she can see it is all delusion? But a progressively darker reality unfolds as we are led inexorably towards a terrible and shocking climax.