A birthday party is planned for Robert, but Rose's contribution to the event surprises those above and below stairs, a new farming venture on the Downton estate comes with dramatic repercussions for Mary, and Edith receives troubling news.

Mary wakes up in bed with Tony Gillingham after their tryst and returns to Downton, where she learns that a building firm want to buy land for a housing estate, to which Robert objects. Violet discovers from her butler Spratt about Mary and Tony but covers for her before summoning her for an explanation. Mary explains to her that she plans to marry Tony but later tells Tom the truth, that she has no intention. In return he confesses that he is considering a move to America. Following the policeman's visit, Anna is perturbed that her ordeal will be revealed, particularly as the animosity between John and Green comes to light. John gives his alibi, that he spent the day in question in York, and Mrs Hughes and Mary agree to collude with this. As Barrow goes to visit his dying father, Baxter tells Cora that she was beguiled into the jewel theft by a cruel footman called Peter Coyle, whom she loved but who fled leaving her to take the blame. Tim's wife wants to bar Edith from seeing Marigold, whilst Rose hosts a benefit for a group of Russian political exiles and Violet is taken aback by one of their number.

Kuragin tells Violet he wants to live with her, someone tries to break up the Atticus Rose wedding, Daisy wants to live in London, and Anna is accused of Green's murder.

Mary endeavors to build bridges with her sister while Edith's secret continues to pose a threat. As Henry settles into the role of husband and stepfather, finding his place at Downton proves more difficult.