When the Countess Narona meets Agnes Lockwood, the woman jilted by her husband-to-be, she feels a great sense of foreboding. After the marriage, she moves with her husband, Lord Montbarry, to Venice. As much as Agnes tries to forget the episode of her broken engagement, her fate and that of the Countess seem to be inextricably woven. Both are relentlessly drawn to the Palace Hotel in Venice for a final and dramatic encounter, in the room where more than past emotions resurface to haunt them.

Loosely based on a case from the annals of French crime, the horror of this mystery comes through the invention of one of the classic Victorian "sensation" novelists, Wilkie Collins, who also wrote The Moonstone and The Woman in White.