Maggie Buckley

In the novel Peril at End House, Magdala “Maggie” Buckley was a cousin, and namesake (Magdala Buckley), of Nick Buckley. Her parents are Giles and Jean.

She was described as a "quiet girl, pretty in the old-fashioned sense". She had blue eyes, and a pleasant, slow voice. Her mother described her as "quiet and unselfish - always thinking of others".

Spoilers ahead
Initially it was believed that her death was due to a mistaken identity, since she was wearing Nick Buckley's shawl, but later it turned out that that wasn't the case. The intended victim was really Maggie, who had been shot by her cousin Nick. It was her, and not Nick, who was engaged to Michael Seton and stood to inherit.

Agatha Christie's Poirot
In ITV's 1990 film adaptation of Peril at End House, the part of Maggie Buckley is played by Elizabeth Downes. She has only a small speaking part and does a good job of concealing her relationship with Michael Seton.

Agatha Christie's Great Detectives Poirot and Marple
In the NHK anime adaptation The Mystery of End House, Maggie Buckley had a larger role than in the original novel. Here, Nick had already called her down for the party. Her presence was not the suggestion of Poirot. During the party, she actually hinted about her anxiety over Michael Seton's fate in that she told Poirot that she was in no mood to enjoy the fireworks and just wanted to sit quietly by herself. After she had been killed, Poirot went up to Yorkshire to visit her parents and there he learnt more about her background. According to Maggie's mother, Maggie was very shy but was good friends with her cousin Nick who took her everywhere on visits. Maggie was also an avid letter writer and her mother showed Poirot drawer full of letters, most of the envelopes seemed to come from Nick. Maggie's father also showed Poirot Maggie's tombstone being carved. From this, Poirot made the startling realization that her name was actually "Magdala". After the denouement, Nick made a confession and revealed the rest of Maggie's story. Nick had been in love with Michael but she had brought Maggie to an airport to meet him and there the two had fallen in love with each other instead. Maggie's father did not like rich people and in any case he had wanted Maggie to marry the curate in his church. He therefore would not have approved of Maggie getting engaged to Michael Seton. As a result, Maggie had to keep her engagement secret. She also had to ask Nick to act as the go-between for the letters between her and Seton, and this explained the large number of envelopes sent by Nick. Despite the large role, the voice actress behind the character of Maggie Buckley is not credited.

Les Petits Meurtres d'Agatha Christie
In La maison du péril, the France Télévisions and Escazal films adaptation of the novel, the parallel character is Eleonore.