Helen MacKenzie

In the novel A Pocket Full of Rye, Mrs Helen MacKenzie is the widow of Mr MacKenzie and the mother of Donald and Ruby, both of whom she fostered to hate Rex Fortescue. She is living in Pinewood Private Sanatorium, and doesn't speak with her daughter anymore. She is sixty-three, though she looks younger.

She is described as having "pale blue, rather vacant-looking eyes, and a weak, indeterminate chin". She has grey hair and a long upper lip that occasionally twitches.

Mrs MacKenzie tells Inspector Neele that the Blackbird Mine was her husband's, and he went to Rex Fortescue for money to capitalise it. She says that no one knows how her husband died or where he is buried, and all anyone knows is what Rex said. She is convinced that Rex was responsible for her husband's death. Therefore, she made Donald and Ruby swear every night that they would kill Rex.

Mrs MacKenzie also tells Inspector Neele that Donald died at Dunkirk, and that she no longer has a daughter. She says that Ruby did not keep faith, and that there is no such person as Ruby MacKenzie anymore.

Portrayals
Mrs Mackenzie does not appear in the BBC 1985 adaptation of the novel which formed part of the Miss Marple series. She is mentioned several times and Miss Marple does go to see her (off screen) but she tells Inspector Neele there is no need to question her as her mind is all gone. In this version, Mrs Mackenzie is apparently not hostile to her daughter who apparently does visit her at the sanatorium.

In the ITV 2008 adaptation of the novel (Episode 1, Season 4 of Agatha Christie's Marple), the part of Mrs Mackenzie is played by Prunella Scales. Here, as in the original novel, she is very lucid and tells Miss Marple the background to the Blackbird mine. She also repeats the point in the book that "she has no daughter" because she had broken faith.