It's the summer season in London and as part of Rose's 'coming out' she is to be presented at Buckingham Palace. The Crawley Family and most of the servants are at Grantham House, their London residence, preparing for the busy social program. Not one to miss such a grand occasion, Cora's mother Martha Levinson (Shirley MacLaine) makes the journey from New York with her playboy son Harold (Paul Giamatti), fresh from his recent brush with the law. Both outspoken and larger-than-life, they make quite an impression amongst certain members of London's high society. Isobel finds herself with an admirer while Edith is wrestling with a moral dilemma. Downstairs, Daisy gets an unexpected invitation and Carson treats the staff to a special day out. When the Crawleys are implicated in a scandal that threatens to engulf the monarchy, Robert will go to great lengths to protect the royal family, and his own.