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, 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.

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.

Violet's new maid doesn't seem to be working out, Kuragin reveals he still loves Violet, Anna realizes Bates' innocence, and Thomas reveals a secret to Baxter.

What begins as a happy day out for the family and servants ends in panic and leaves Robert with a difficult decision to make.