Isobel finds herself at odds with Violet. Mary is introduced to a potential suitor but wants to be with Matthew. Anna works out who stole a valuable snuff box. O'Brien plans a way for Edith to get even with Mary.

Sybil puts herself in danger when a fight breaks out. Sybil's sisters notice Matthew's feelings for her. Mary is surprised by a marriage proposal. Bates clears his name over the missing wine but resigns rather than name the real culprit.

Cora's pregnancy throws the inheritance issue into doubt. Matthew must wait for an answer to his wedding proposal. O'Brien discovers more compromising information about Bates. Thomas leaves.

Cora’s mother sweeps into Downton for Matthew and Mary’s wedding, but with the couple’s relationship under strain will they even make it to the altar? New footman Alfred strives to meet Carson’s high standards, under the watchful eye of his aunt O’Brien. Robert’s shocking news brings financial worries to the fore, on an unprecedented scale. Might he lose Downton itself and all it stands for?

The estate's future is hanging in the balance and Mary is hoping to receive a bailout from grandmother Martha. Violet also attempts to help her make sure that Downton puts on a bigger show than ever before with a grand party for friends and neighbours. Mrs Hughes gets some news that worries her. O'Brien's attempts to boost Alfred's progress are met with disapproval from Thomas.

Edith's wedding day arrives but will her enthusiasm be able to convince the family that Strallan's age doesn't really matter. Mrs Hughes awaits her results. Anna manages to make a breakthrough as she tries to help Bates. Mary decides to take matters into her own hands to secure the estate's future.