The Moving Finger recap

While Jerry Burton recuperates in Lymstock with his sister Joanna, anonymous letters accuse residents of secret misconduct. A letter to Mona Symmington is followed by her apparent suicide, and the later murder of a maid proves that the danger is not merely malicious gossip. Miss Marple realizes the wide distribution of letters was meant to hide a single purpose. Mona's husband, Richard Symmington, manufactured the campaign and murdered her so he could be free to marry the governess, Elsie Holland; he also killed Agnes Woddell when she could expose his movements. He then tries to murder and frame his stepdaughter Megan, but a police trap and Jerry's intervention stop him. Symmington is arrested, Jerry and Megan plan a future together, and Joanna is paired with Dr Griffith.

After an air accident, Jerry Burton rents Little Furze in the village of Lymstock and moves there with his sister Joanna to recover. Soon after their arrival they receive a crudely abusive anonymous letter questioning their relationship. They learn that similar poison-pen messages have reached many local households. The Burtons meet solicitor Richard Symmington, his wife Mona, Mona's unhappy daughter Megan, the family's governess Elsie Holland, Dr Owen Griffith and his energetic sister Aimée, and the Calthrops at the vicarage. The police quietly begin examining the letters, but their mixture of invented scandal and local knowledge leaves almost every resident open to suspicion.

Mona Symmington receives a letter casting doubt on the legitimacy of one of her children and is found dead from cyanide, with a message interpreted as a suicide note. The village assumes the poison-pen writer has driven her to death. Jerry grows protective of Megan, who is treated as an awkward burden in her own home, while Joanna becomes closer to Dr Griffith. Investigators study typewriters, paper, envelopes, and the social knowledge behind the accusations. Agnes Woddell, a maid in the Symmington household, remembers something that disturbs her and tries to consult another servant before she can give a clear account.

Agnes is found murdered, confirming that someone is using violence to protect a secret. Police suspicion turns toward a local woman whose access and habits seem compatible with the letters, but the explanation does not account convincingly for both deaths. Mrs Calthrop calls in Miss Marple, who focuses less on handwriting and village gossip than on the practical result produced by the campaign. She argues that the flood of accusations may exist to disguise one targeted crime. Jerry helps Megan change how she presents herself and recognize her own value, yet her position in the Symmington family leaves her exposed as the investigation approaches the household again.

Miss Marple identifies Richard Symmington as the author of the poison-pen campaign and the killer. He used indiscriminate letters to create a believable atmosphere for Mona's supposed suicide, but he had murdered his wife so that he could pursue Elsie Holland. Agnes Woddell had noticed evidence that undermined his account, and he killed her to preserve it. Knowing that Megan remains dangerous to him, Miss Marple and the police allow her to serve as bait. Symmington tries to poison Megan and arrange the evidence so she will appear responsible for the letters, but Jerry reaches her and the police intervene. Symmington is arrested. Jerry and Megan recognize their love, and Joanna's relationship with Dr Griffith also promises a new beginning.

Miss Marple recognizes that the anonymous campaign was camouflage for a planned domestic murder, not the work of a compulsive village gossip. Richard Symmington created the letters, killed his wife Mona, and arranged her death as a suicide so that he could eventually marry Elsie Holland. Agnes Woddell noticed a fact that threatened his false chronology, so he killed her as well. Miss Marple and the police use Megan as bait: when Symmington attempts to poison her and leave evidence that would blame her for the letters, Jerry intervenes and the trap closes. Symmington is arrested. Jerry acknowledges his love for Megan, who has gained confidence and independence, while Joanna and Dr Owen Griffith form their own attachment.