The scenario contains many Gainsborough ingredients, but with important differences. It is set in the present, and returns Lockwood to the kind of pre-war ingénue role she had enjoyed before The Wicked Lady (1945) revised her screen image: until she takes charge in the final minutes she is strictly a character that things happen to.
However ripe the plot, writer-director Charles Bennett is subtler in his effects and devices than most critics allow. He begins with a flashback explaining how Lydia (Lockwood) has become both blind and a nun; we confidently expect this to constitute the entire film. Interestingly it proves a mere prologue: soon we return to the nunnery, from which the film proceeds in the present tense. Lydia's sudden descent into blindness is conveyed (appropriately enough) by an iris shot, the screen closing on her terrified face as if the world is darkening and constricting around her. Reflecting her heightened sense of hearing, the soundtrack effectively employs ambient music, echoes and natural sounds. And a remarkable degree of suspense is achieved in the scene in which Kathleen Byron (at her Black Narcissus nutcase best) attemptspts to drown Lydia, with its undercurrent of subdued eroticism.
There are also some interesting plot echoes: doctors tell Lydia that the operation to save her sight may leave her "without a mind"; at the climax the confronted villains bluff, "I hope that in regaining your sight you have not lost your mind". And - in a scene strikingly reminiscent of one in The Wicked Lady - Byron, riding furiously on horseback, her face reflecting both hatred and exhilaration, only just avoids plummeting over a cliff, prefiguring her death in identical circumstances (albeit in a car) at the film's end.
Bennett had co-written many of Hitchcock's finest movies, and this film is highly reminiscent of Rebecca (1940) in its settings (an imposing house near a raging coastline), and plot motifs (a commoner's marriage to a wealthy landowner is deliberately strained by a hate-filled third party). The climax even involves an attempt to make Lydia fall from one of the chateau's windows.