In the novel Evil Under the Sun, Rosamund Anne Darnley is a fashionable dressmaker, under the name Rose Mond. She is also a childhood friend of Kenneth Marshall. They meet again during a holiday at a secluded hotel in Devon. She is four years younger than Kenneth.
The register at the Jolly Roger Hotel gives Miss Darnley's address as 8 Cardigan Court, W1. She cinducts her dressmaking business at 622 Brook Street.
Poirot admires Miss Darnley, because he likes her distinction, "the graceful lines of her figure", and the "alert proud carriage of her head". She has dark hair which is styled in "neat sleek waves", and her smile has an "ironic quality". Her hands are well-shaped, "beautifully moulded with very long fingers".
Miss Darnley tells Poirot that she had a very English childhood, in a "big shabby house" in the country. She also mentions some childhood memories including horses, dogs, lack of money, and "evening dresses that went on from year to year".
According to Captain Marshall, Miss Darnley used to get into "the most frightful rages" as a child, and once flew at him in a temper, half-choking him. He also mentions an incident when she nearly killed a boy about a dog, when she had hung on to his throat and would not let go.
In her adult life, Miss Darnley enjoys "the artistic satisfaction of the successful creative artist" and "the financial satisfaction of the successful business woman". She also says that she is well off, has a good figure, a "passable face", and a "not too malicious tongue".
Miss Darnley asks Captain Marshall why he does not divorce his wife, Arlena. She tells him that Arlena is "pretty notorious", that Arlena is not good for his daughter, Linda, and that people are fixing up divorces all the time.
On the morning of the murder, Linda asks Miss Darnley to go to Gull Cove with her and Christine Redfern. However, Miss Darnley says that she is going to Sunny Ledge with a book, instead. Later that day, she plays tennis with Christine, Captain Marshall, and Mr Gardener.
While conducting a search of the hotel guests' rooms, Poirot notes "the expensive simplicity" of Miss Darnley's toilet set, and the scent of the expensive perfume she uses.
Miss Darnley later tells Colonel Weston, Poirot and Inspector Colgate that she did leave Sunny Ledge and returned to the hotel on the morning of the murder, at about a quarter past eleven. She tells them that she had looked in on Captain Marshall and seen him typing, and had intended to tell him to come outside. However, he was typing so vigorously and looking so concentrated that she went away, and he did not see her. Captain Marshall later says that he did see her, in the mirror above the table.
It is later revealed that Miss Darnley had lied about returning to the hotel and seeing Captain Marshall typing in his room. Captain Marshall had also lied about seeing her in the mirror.
Miss Darnley later tells Captain Marshall that his alibi seemed "a bit on the light side", so she made up the story about seeing him typing. She explains that she did not know what he really felt about Arlena, and she thought if he had really believed in her but suddenly found out that she was having an affair, that he might have gone mad with rage and killed her.
Miss Darnley asks Captain Marshall if he is going to ask her to marry him, or if he is going to wait six months. He asks her to give up her dressmaking business and live in the country with him. She says that she has wanted to live in the country all her life.
Les Petits Meurtres d'Agatha Christie
In Ding Dingue Dong, the French Televisions adaptation for the Les Petits Meurtres d'Agatha Christie series, the closest parallel character is Alice Avril. She is attracted to Louis Rodier, the Kenneth Marshall parallel. She also befriends his daughter Adele Rodier and at one point she also stops her from attempting to commit suicide. However some roles are split and shared with Dominique Lebrun, the Mrs Castle parallel.