The Voice in the Dark is a short story written by Agatha Christie.
Mr Satterthwaite is back on the French Riviera and enjoying the sunshine at Cannes with Lady Barbara Stranleigh, someone he has known since his own youth. She is, as Satterthwaite describes her himself, "beautiful, unscrupulous, completely callous, interested solely in herself." She has been married four times and came into the family title after a series of deaths and tragedies some forty years before, the final one of which was a shipwreck of a vessel named the Uralia which sank off the coast of New Zealand, killing her elder sister, Beatrice.
Lady Stranleigh confesses she is worried about Margery, the daughter of one of her marriages. She is a sturdy outdoors sort of girl who prefers Fox hunting to the Riviera or balls and who has in the past few months been reporting hearing voices in the night at their family home of Abbot's Mede back in Wiltshire. The house doesn't have the reputation of being haunted and Lady Stranleigh asks a reluctant Satterthwaite to go back to England and use psychic researchers to find out what is going on. On the train ride home, Satterthwaite is delighted to meet up with Mr Quin and he outlines the story to him. Quin tells him that he will be staying near Abbot's Mede at the “Bells and Motley” inn where the two met previously and, if Satterthwaite is in need of help, he should call on him there.
At Abbot's Mede, Satterthwaite meets Margery who tells him that for the past couple of months she has heard the voices in the dark of her bedroom. Sometimes it is a whisper, sometimes a clear voice telling her to, "Give back what is not yours. Give back what you have stolen." On each occasion she has switched on the light but no one is there. She has now taken to having her mother's maid, Alice Clayton, sleep in the next room but she hasn't heard the voices, even though they have been clear to Margery. Events reached a more sinister turn the previous night when Margery had a dream that a spike was entering her throat and woke to find that some sharp object was indeed being pressed against her neck and the voice murmured, "You have stolen what is mine. This is death!" Margery screamed and Clayton ran into the dark room, feeling something brush past her as she did so.
Satterthwaite speaks to Clayton, an elderly blue-eyed, grey-haired woman who was also a survivor of the Uralia and who confesses that she put Margery's claims down to imagination until the events of last night. Staying as guests in the house are an old friend of Margery's, Marcia Keane, and a family cousin, Roley Vavasour who have both been staying at the house since the time when the voices started, thus they attract Satterthwaite's suspicions.
The post arrives at the house and among the items is a letter from Lady Stranleigh thanking Margery for the chocolates she sent and telling her that she has been laid low by a dose of food poisoning. Margery tells Satterthwaite she never sent her mother chocolates. Aside from the long-term guests in the house, there is also a Mrs Casson and a Mrs Lloyd, the former a spiritualist and the latter a medium, brought in by Roley, who organises a séance. After speaking to the medium's spirit guide of a Red Indian Cherokee, the voice of Lady Stranleigh's sister, Beatrice, comes through. Satterthwaite tries her with a question which he knows only she will know the answer to, but she answers correctly. 'Beatrice' repeats "Give back what is not yours."
Somewhat shaken by this event, Satterthwaite questions Margery about Roley and finds out that he is the heir to the title and estates should her mother die. He has asked Margery to marry him but she has refused, being engaged to a local curate, somewhat against her mother's wishes.
Lady Stranleigh sends a telegram to say that she is arriving home early, so Satterthwaite retires from the matter and returns to London. However, he is shocked to read in the morning paper that Lady Stranleigh has died at Abbot's Mede, being found dead in her bath from drowning. He returns to Wiltshire but makes for the "Bells and Motley" where, as promised, he finds Mr Quin. His friend listens to the entire tale but tells Satterthwaite that he has solved these matters himself before when, as now, he has been in full possession of the facts and he can do so now.
Satterthwaite returns to Abbot's Mede and finds a saddened Margery. She has drawn up a new will and asks him to be the second witness, Clayton being the first. Satterthwaite is about to sign when he sees Clayton's first name – Alice – and realises she is the same maid who, many years earlier, he had kissed in hotel's passage. He remembers she had brown eyes and, stunned, tells Margery that the woman she knows as Clayton, who has blue eyes, must be her Aunt Beatrice. "Clayton" has a scar where she was struck on the head during the sinking of the Uralia and he imagines this blow destroyed her memory at the time. Her avaricious sister used the opportunity to swap her identity and inherit the family money and it is only now that her memory is returning, but in her mentally unhinged state she began her persecution of her niece. The two go to Clayton's room but find the woman dead, probably from heart failure. As Satterthwaite says, "Perhaps it is best that way."