Relations between Robert and Cora continue to be strained. Blake's scheming starts to come to fruition when Mary is unexpectedly pitted against her love rival. Edith receives some terrible news and decides to take drastic action. Following a mysterious tip off, Baxter becomes embroiled in the investigation of Green's death. Thomas' condition deteriorates, prompting him to finally reveal the truth to Baxter. Love is in the air for more than one member of the Crawley family.

Rosamund shows up at Downton following Edith's surprise departure. Rose is pleased to introduce Atticus and his parents to everyone. Anna and Bates think about a fresh start, now that that their problems seem to be behind them. Molesley is worried after Daisy becoming disillusioned with her studies. Mary and Blake seize a chance to send Gillingham a strong message.

Preparations are under way for Rose's wedding, but family tensions on both sides threaten to derail proceedings. Edith's arrangement with Marigold is happily working out, but how long can she and Cora conceal the truth from Robert? Denker reveals an unexpected side to her personality, which causes trouble for more than one of the servants. With the war memorial due to be unveiled, Mrs Patmore is still upset, but Robert has something up his sleeve. Branson comes to a heart-wrenching decision, and the storm clouds that have been gathering over Anna and Bates finally burst.

It's grouse shooting season and Rose’s father-in-law, Lord Sinderby, has rented out Brancaster Castle in Northumberland and invited the Crawley family to a shooting party. While good sport is enjoyed, Stowell has an axe to grind and a scandalous secret threatens to undermine the holiday. Surprises are in store as the families become better acquainted with each other and some new faces arrive on the scene.