Lord Sinderby has rented out Brancaster Castle and invited the Crawley family for a shooting party. Stowell has a axe to grind as the rest of the family enjoy the fun. The families get better acquainted with one another. Back at Downton the servants hold the fort. Anna faces up to a uncertain future behind bars, Bates decides to take drastic action to clear her name. Carson and Mrs Hughes consider going into business together. Baxter and Molesley work together on a joint plan.
Local plans for a war memorial see Carson pitted against Robert and Mrs Hughes. Jimmy receives some female attention that causes him major problems. Baxter is issued with an ultimatum. Tom's burgeoning friendship with Sarah Dunning causes Robert concern. Mary feels ready to try and find love again. Edith and Drewe's special arrangement starts to crumble as she increasingly finds it hard to keep her emotions in check resulting in some disastrous consequences for everyone.
Robert is left with a difficult decision to make. Mrs Patmore has an idea which might solve everything as Daisy continues to struggle with her studies. Thomas has issues with Baxter, however will his meddling ruin her friendship with Molesley? Rose tries to convince Robert of the positives of a wireless at Downton. Lord Merton continues to pursue Isobel while Mary puts her reputation in danger when Anna is made an accomplice.
Robert is left furious when things don't go as planned. Mary's undercover assignment is nearly blown. Violet is quick to save the day. The events surrounding Green's death are under scrutiny. Mrs Patmore is left devastated when old wounds are opened. Branson receives a proposition regarding the future of the Downton estate.
Sarah Bunting continues to cause waves above stairs, but this time she may have gone too far. On returning to Downton, Thomas suffers an inexplicable illness and Baxter suspects there's more to it than he's letting on. Violet reveals to Isobel the surprising truth of her past with Prince Kuragin. Mary comes to a decision concerning Lord Gillingham, but things don't go quite as planned. When Rose's father returns to Downton, he breaks news that will shock the whole family
Simon Bricker returns to Downton to discuss the painting with Cora. Branson makes a difficult decision about Sarah Bunting. Rose encounters a handsome stranger. Determined to stop Isobel making the wrong decision about Lord Merton, Violet enlists the help of Doctor Clarkson. Charles Blake surprises Mary with a cunning plan to help her get exactly what she wants. Mrs Patmore seeks Carson's advice on a financial matter. Inspector Vyner returns with some ominous words of warning for Anna.
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.