Mirrors

Mirrors occur as plot devices in several Agatha Christie stories. Very often viewing something in a mirror leads to a distortion or a mistaken inference about what has been seen.

Stories where mirrors are a plot device

 * In a Glass Darkly - A man with a scar on the left of his face is seen strangling a woman. Years later the witness realises that the face was reflected in a mirror.
 * Dumb Witness - In the dark a woman sees someone wearing a monogram brooch. Poirot deducts that it could only have been seen if reflected in a mirror.
 * Cat Among the Pigeons - A woman on a hotel balcony uses a hand mirror to see into the next room. Reflected in a mirror in that room she sees someone doing something strange.
 * Dead Man's Mirror - here the reflection is not significant, but the way it is damaged by a bullet is.