Handedness

In some of Christie's stories, whether a person is left-handed or right-handed is critical in the solution of the crime.

Stories where the handedness of a person is used as a plot device

 * The Market Basing Mystery
 * Murder in the Mews
 * The Idol House of Astarte
 * Towards Zero - the murder victim appeared to have been bludgeoned in such a way as made it very inconvenient for a right-handed person to have done it.

Adaptations where the handedness of a person is used as a plot device

 * The Affair at the Victory Ball (Agatha Christie's Poirot episode) - in the film adaptation only, the murderer was left-handed and this enables Poirot to unmask him. This plot device does not occur in the original story.
 * Dead Man's Mirror (Agatha Christie's Poirot episode) - the murder victim was right-handed but the gun was in his left hand and the wound on the left of the head. Thus Poirot proved to Japp that it could not have been a suicide. This plot device does not occur in the original story. There Poirot concluded it could not be a suicide based solely on the psychology of the murdered man.
 * The Mirror Crack'd - In the film within the film, Murder at Midnight, the murderer is left handed. Since the film projector in the village hall breaks before the audience can see the end of the film, Miss Marple reveals the solution.
 * At Bertram's Hotel (Agatha Christie's Marple episode)
 * Jack Britten and Joel Britten were twins and could impersonate each other but Miss Marple identified who was whom because Jack was left-handed and Joel right-handed and wore their wrist watches on different hands.
 * Brigit Milford could not use her right arm and hence held a gun in the left. This gave her away when she tried to impersonate someone right-handed.