Tim Drewe guesses the parentage of Marigold, Mary receives another proposal from Tony, Violet plays matchmaker, Thomas continues to press Baxter for information with blackmail, and a flash fire threatens the mansion.
James leaves Downton, Mary has a weekend rendezvous with Gillingham, Carson and the Earl disagree for the site of the War memorial, a wireless becomes part of Downton life, and Edith becomes Marigold's godmother.
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, ...
The Countess confesses her past with Prince Kuragin, Lord Merton proposes to Isobel, Rose's parents are divorcing, Lord Grantham becomes jealous of Simon, and Lady Mary tells Gillingham she won't marry him.
Tom ends his relationship with Sarah, Rose meets a young man of Russian descent, Rosamund's visit to Marigold has consequences, Mrs. Patmore asks advice for her inheritance, and Simon Bricker expresses his love for Cora.