April 1912 . The family and staff of Downton are shocked when they find that the heir to the title and fiancé of the Earl's daughter Mary perished on the Titanic, and the Earl hires a disabled army comrade as valet.
September 1912. The new legal heir to Downton, lawyer Matthew Crawley, arrives with his mother, Isobel, to live on the estate. However, they are resented as usurpers and interlopers by both upstairs and downstairs.
Gwen's ambitions to leave service and become a secretary are discouraged, Bates takes painful steps to overcome his limp, and a dashing Turkish diplomat visiting Downton seems to work his charms on everyone - especially Mary.
Downstairs, the steadfast housekeeper, Mrs. Hughes, faces a life-altering decision when a former love interest reappears and proposes marriage, offering her a future away from a life in service. Meanwhile, upstairs, the Countess of Grantham hires Matthew Crawley to find a legal loophole in the entail.
Bates sees Thomas stealing a bottle of wine, the footman tries to frame him for petty theft, and Mrs. Crawley tries to convince the Dowager Countess to surrender her annual entitlement prize for best bloom in the village.
O'Brien and Thomas continue their efforts to frame Bates, Mary falls in love with Matthew, and Sybil is injured in a political disturbance and Branson is blamed.
July 1914. Mary learns it was Edith who informed the ambassador know about Pamuk's death, Cora announces her pregnancy, and Thomas and O'Brien hatch new slanders against Bates as war clouds loom.
