Lady Rose MacClare[1] (Born in Autumn 1902[2]) is the youngest child of Hugh and Susan MacClare, the niece of Agatha and Louisa, the younger sister of James and Annabelle, the sister-in-law of Annabelle's husband, the granddaughter or great niece of Roberta and the great-niece of Violet Crawley. In Autumn 1920, she visits Downton Abbey and stays with Violet in the Dower House.
Violet says she is eighteen, meaning she was born in or before Autumn 1902; Violet was told that Rose "hates London" which is why she is coming to stay with her, until her father can finish with his work in London and they can go to their country estate in Scotland. However, when she arrives and learns that Lady Edith Crawley is planning a trip to London, she eagerly wishes to go too, much to Violet's surprise. Rose's explanation is that she is planning a secret surprise for her mother, but does not say what. She asks that no one else mention this.
Later, Matthew Crawley has to go to London. He agrees to stay with Lady Rosamund Painswick, at Eaton Square, as Rose and Edith are doing. Edith tells Matthew that she feels she will need help controlling Rose, out of "instinct."
When they arrive at Rosamund's house, she insists they all dine with her that night at eight o'clock. Immediately after they all go about, Rose makes a phone call, then later is seen getting into a taxi dressed in clothes one would not expect a well-born young lady to wear.
Rose does not show up for dinner, so they begin without her. During dinner, Rosamund's butler brings in the taxi driver who drove her from the house that day. He is returning a scarf that she left in the car. The butler sent him up as he could tell them where he had taken her. He explains Rose first met a gentleman friend and spent two hours with him in Warwick Square, then they went to a club, the Blue Dragon.
Matthew, Edith, and Rosamund go to the Blue Dragon, where they find Rose dancing wildly with and passionately kissing a former employee of her father's named Terence Margadale. Rosamund gets him to admit that he is a married man. Matthew then dances with Rose. She says that Terrance loves her and wants to marry her as soon as he can get a divorce from his horrid wife. Matthew says that men trying to seduced young women often describe their wives as horrid, and she should meet her and decide for herself. He persuades her to return to Rosamund's house, making a deal with her that they won't say anything about her seeing Margadale if she promises not to try to see him again as long as she is staying with them. However, Violet finds out about it anyway after overhearing Rose and Edith talking about keeping a secret. Violet then contacts Rosamund and gets her to tell everything by pretending that Edith had already told her. Rose is then told she is being sent to Scotland with a stodgy old aunt and will be escorted the entire way to keep her from running away to see Terrance.