For over thirty years, the Press had reported on Bess "doing this or that outrageous or extraordinary thing". Her adventures included being a member of the French Resistance during the war, flying solo across the Atlantic, driving racing cars, and saving children from a burning house. It was also said that she had successfully smuggled herself onboard a nuclear submarine for its test voyage.
When Bess was sixteen, she ran away with an Irish groom. Her family went after her, and bought the man off. Bess married Lord Coniston, with whom she had a daughter, Elvira.
When Elvira was two years old, Bess left Lord Coniston. She did not ask for custody of Elvira because she did not think the life she led would be safe for Elvira. She thought it would be better and happier for Elvira to have a conventional English upbringing, and that if Elvira learned to love her, it might be a source of sorrow to her.
Bess later married John Sedgwick. After his death, she married Ridgway Becker, and they divorced three years before the events of the novel. After the divorce, Bess went back to calling herself Sedgwick.
During the events of the novel, there were rumours that Bess and Ladislaus Malinowski were lovers. Bess herself said that she and Ladislaus had been lovers in a casual way, but that she was not in love with him. According to her, the only person she had ever loved was John Sedgwick.
While staying at Bertram's Hotel, Bess recognised Michael Gorman as the Irish groom she had run away with. He mentioned that he had thought of writing to her, and that he had not forgotten. She told him that he had been paid well to keep his mouth shut, and would not get any more money from her.
Bess met Ladislaus Malinowski at the Army & Navy Stores, where they had lunch. Miss Marple saw them, and overheard Bess questioning why Ladislaus had come to Bertram's Hotel.
Later in the novel, after the death of Michael Gorman, Elvira believed that someone was trying to kill her. Bess accompanied Elvira while Chief Inspector Davy was questioning her. When Elvira becomes upset while describing the events leading up to Michael's death, Bess is able to calm her down by speaking to her in a low, firm voice, which she also used for her horses.
It was revealed that Bess and Michael Gorman had been married, and they had never been divorced. At the time, Michael had told her that they were not really married, and that he and his friends had made it up. However, she later realised that the marriage had been real. This meant that her marriages to Lord Coniston, John Sedgwick, and Ridgway Becker were all not legal.
It was further revealed that Bess was the leader of the gang that was carrying out large-scale robberies. She admitted to this, saying that it was fun for her to plan the robberies and carry them out. She also confessed to shooting Michael. But the last confession had not been truth. She took the blame to protect her daughter, who was the real killer.
Bess attempted to escape arrest by going out the window of her room at Bertram's Hotel, climbing up a drainpipe, and onto the roof. She was able to make it to her car, which was a Mercedes-Otto. However, she was killed when she accidentally crashed into some park railings.