In the novel Peril at End House, Magdala “Nick” Buckley is a young woman living at End House, near St. Loo. Hercule Poirot believes someone is trying to kill her. She has the same name, Magdala Buckley, as her cousin.
Nick has dark hair, and an elfin appearance. She is described as having a "small, vivid face, pansy shaped", and "enormous dark-blue eyes".
Nick's mother died when she was a baby, and her father died of pneumonia in 1919. She lived at End House with her grandfather, Nicholas Buckley. She was fond of him, and went everywhere with him, so people called them Old Nick and Young Nick.
Nick's grandfather died when she was sixteen, six years before the events of the novel. Three years after that, her older brother Gerald was killed in a traffic accident, and so Nick inherited End House. She loved the place, and was described as having a "fanatical devotion to the house".
Plot [spoilers ahead]
Poirot becomes interested in Nick's case when she tells him that she has had three near escapes from death in three days. First, a heavy picture hanging over her bed fell during the night, but she had happened to hear a door banging somewhere downstairs, and had gotten up to close it, and so she escaped. Second, when she was going down the cliff path towards the sea, a boulder came rolling down, just missing her. Third, something went wrong with the brakes of her car, which would have caused her to lose control of the car had she gone out of the gate and driven down the hill. However, she turned back towards the house, and crashed into the laurel hedge, and so was unhurt. When Poirot finds a bullet that appears to have been fired at Nick while she was talking to him on the terrace of the Majestic hotel, he becomes convinced that her life is in danger.
Nick hosts a Regatta party at End House, which is attended by many guests, including her cousins Maggie Buckley and Charles Vyse, and friends Freddie Rice, and Jim Lazarus. While everyone is outside watching the fireworks, Nick and Maggie return to the house to get their coats. Maggie is unable to find hers, and so takes the shawl which Nick had been wearing.
Later, when Maggie is found dead, wearing Nick's shawl, it is thought that this is a case of mistaken identity, and the murderer actually meant to kill Nick. Poirot sends Nick to a nursing home, for her safety.
Poirot discovers that Nick was secretly engaged to Captain Michael Seton, and that with his death, she has inherited his fortune. This is thought to be the murderer's motive for killing Nick.
While in the nursing home, Nick suffers from cocaine poisoning, after eating chocolates which appeared to have been sent by Poirot. She survives, but Poirot leads everyone to believe that she is dead, in order to lure the murderer out.
It is later revealed that Nick was the one who murdered Maggie. It was Maggie, not Nick, who was engaged to Captain Michael Seton, and would inherit his fortune. Nick wanted the money for herself, and so planned to pose as Seton's fiancee, since she shared the same name, Magdala Buckley, as Maggie.
Nick staged the "accidents" she had described to Poirot, in order to make it appear as though she was the one whose life was being threatened.
On the night of the party, she wore a black dress as she knew that Maggie would be wearing black. She also lent Maggie the red shawl she had been wearing herself, earlier in the evening. This was to make Maggie's death seem like a case of mistaken identity. She shot Maggie, and hid the gun in a secret compartment in the drawing room of End House.
Poirot also suggests that Nick and Freddie's wrist-watches contain cocaine, which George Challenger supplies. This was how Nick laced the chocolate with cocaine, while in the nursing home.
Before she is arrested, Nick asks Freddie for her wrist-watch as a souvenir. Poirot suspects that she will commit suicide by ingesting a full dose of cocaine.
Agatha Christie's Poirot
Nick Buckley is played by Polly Walker in the film adaptation of Peril at End House in Series 2 of ITV's Agatha Christie's Poirot drama series. The portrayal is fairly close to that in the original novel.
The Mystery of End House
Nick Buckley is voiced by Misaki Itô in the NHK anime adaptation The Mystery of End House. There is a bit more backstory than in the original. Nick was originally in love with Seton but had brought Maggie to the airport to meet him and he fell in love with her there. This was dramatised in a scene. Maggie's father disliked rich people and wanted her to marry the curate of his church. So Maggie asked Nick to be the go-between for her letters to and from Seton. Poirot actually visits Maggie's family in Yorkshire and discovers a large number of letters from Nick among Maggie's things. As is common in many Japanese anime adaptations, the perpetrator makes a full confession, usually with some contrition. Here, after Poirot's denouement, Nick confesses but justified it on the grounds that she loved Seton first, and probably more than Maggies. Also Maggie would not know what to do with the money. Nick would have turned End House into a memorial for him. There is no sideplot of George Challenger peddling drugs so the plot element of asking for the wristwatch is omitted.