The year is 1912 and RMS Titanic has just gone down, taking with it Lord Grantham's heir, James Crawley, and his son, Patrick. A new heir is needed. The country is teetering on the brink of the First World War.
With the arrival of Matthew Crawley imminent everyone is anxious. Matthew finds it hard to settle into his new life in Downton and his mother Isobel is also soon at odds with Violet. Carson is shocked to be confronted by his past. Gwen has a secret correspondent.
Cora's efforts to matchmake end up being dashed when Mary ends up not being smitten not by Evelyn Napier, but by his friend, Kemal Pamuk instead. Their attraction ends up sparking a series of events whose consequences end up rippling through the entire household. Bates takes action to help cure his limp.
After the fair shows up in the village, Mrs Hughes finds herself the main focus of speculation when she meets a former suitor who makes her question her position. Violet and Isobel clash over a medical ailment affecting Molesley. Carson is concerned there is a thief at work in the grounds.
The village gets ready for the annual flower show and Isobel finds herself at odds with Violet. Mary is introduced to a potential suitor but she wants to be with Matthew. Anna works out who is responsible when a valuable snuff box goes missing. O'Brien plans a way for Edith to take get even with Mary.
Sybil's ends up putting herself danger when a fight breaks out at an election results meeting. Matthew' feelings towards Sybil are noticed by her sisters, but it is Mary who ends up being surprised to receive a marriage proposal. Bates manages to clear his name over the missing wine but he decides to resign rather than name the real culprit who is responsible.
News of Cora's pregnancy ends up throwing the inheritance issue into doubt. Mary tells Matthew that he is going to have to wait for an answer to his wedding proposal. O'Brien discovers more compromising information about Bates which he gives to the Earl but he is surprised by his response. Thomas ends up leaving.