Set in November 1916, the episode begins with the arrival of Ethel, a new housemaid, and the first appearance of John Bates' wife. With Matthew and Thomas fighting in France, those left behind at Downton organise a benefit concert to help fund the local hospital. Lady Mary receives shocking news. Branson reveals his feelings to Sybil who wants to train as a nurse

Set in April 1917 and with many of the male staff serving in the war, Carson finds himself under pressure to make sure that duties are carried out to his exacting standard. He ends up finding himself forced to accept female staff serving in the dining room. Robert needs to hire a new valet and ends up employing Lang, who has just returned from the war. William is happy after he receives an important letter. Mrs Patmore finds out some devastating news about her soldier nephew. Thomas returns from the war and begins work alongside Lady Sybil in the local hospital. After a patient is brought in suffering with gas blindness Thomas finds himself becoming attached to the young Lieutenant. Molesley takes an interest in Anna. Matthew learns of his temporary transfer back to England for a recruitment drive in the north whilst fighting in the trenches. Carson advises Mary that if she still loves Matthew she needs to tell him before it is too late. [4] Meanwhile Lavinia is reunited with an unwelcome face from her past.

Set circa July 1917. The village hospital is not large enough to accommodate the large influx of wounded soldiers coming back from the front so Downton is turned into a convalescent home for many of them. O'Brien is shocked that Isobel Crawley seems to be giving most of the orders while Cora is relegated to the background and suggests that Thomas might be able to aid her from his position at the hospital. Violet strongly believes that Mary and Matthew are still very much in love and so, with the help of Rosamund, tries her best to end Matthew's engagement to Lavinia. She is also still convinced that there is much more to Lavinia's relationship with Sir Richard than meets the eye. Meanwhile, Anna runs into Mr. Bates in the village and they feel they may have a future together but, back at Downton, things are more highly charged as William asks a question of Daisy just before heading off to war and Mrs. Patmore reacts very badly to a chance remark. And what exactly is Branson up to? Whatever it is, it looks like it may cause trouble for Lord Grantham.

Set in early 1918. Ethel's flirting with Major Bryant lands her in trouble as preparations get under way for a concert at Downton. Tensions flare between Isobel and Cora, Edith receives worrying news about Matthew and William, while Branson declares his feelings for Sybil. Robert receives a letter from Carlisle, which causes him concern forcing an uncomfortable conversation with Mary. Mrs Bird's soup kitchen receives a helping hand from Daisy and Mrs Patmore. In the servants’ quarters Mrs Hughes makes a shocking discovery that ends in tears for one member of staff.

Set in mid 1918. 16 October 2011 Set in mid 1918. Robert receives some shocking news from the front. William has sustained serious damage to his lungs and is unable to recover, prompting him to ask Daisy to marry him before he dies. Meanwhile, Matthew has suffered damage to his spinal cord, causing him to lose mobility and feeling in his legs. Worse still, he subsequently learns that his injuries have made him impotent. Lavinia insists that this changes nothing and that she is not concerned about having a sexual relationship and children but only wants to care for him. However Matthew tells her to leave and forget him, while Mary attempts to nurse him back to health. Despite not truly loving William, Daisy is pushed into marrying him by Mrs Patmore, who wants William to die happy, and by William's wishes that Daisy is left with a widow's pension so that she can be looked after. They marry while William is bed-ridden, surrounded by the other staff, Edith and the Dowager Countess. William dies in his sleep, not long after, with Daisy by his side. Bates is taken aback when Vera threatens to expose old secrets about Mary and Pamuk's death. When Mary discovers this, she confesses everything to Richard Carlisle and asks him to help. While he accepts, he does so expecting her to marry him, as she is now in his debt, even going as far to announce their engagement in the newspaper without informing her, leaving Mary in a difficult position. Carlisle tricks Vera into signing a contract, preventing her from selling the story to anyone else, but on finding out she warns Bates that she will still bring him down. A new maid, Jane is hired

Set in November 1918. A Canadian officer is brought to Downton for recuperation and disrupts everything. Ethel hears distressing news, Bates makes another attempt to settle matters with Vera, while Carson receives a tempting offer. Matthew gets used to life in a wheelchair with Mary as his round-the-clock carer. The war ends with Armistice not long after.

Set in 1919. As the residents try to return to normal life following the armistice, Matthew begins to suspect that he can feel his legs. Then one day, seeing Lavinia drop a heavy tray, he suddenly gets up from his chair. Major Clarkson admits that he had been informed of this possibility by another physician but was sceptical about it himself and didn't want to raise their hopes. As a result of his recovery Matthew announces that he and Lavinia intend to be married soon. This Violet to inform him that Mary is still in love with him but Matthew feels obliged to marry Lavinia as she was prepared to sacrifice her life for him. Meanwhile, Richard Carlisle distresses Anna by asking her to spy on Mary and his behaviour leads Carson to reject his offer of employment. Bates reels from the news about Vera after it appears that she committed suicide in order to frame him. Thomas embarks on a new money-making scheme in the post-war black market. Robert is attracted to the new maid Jane and illicitly kisses her. Contemplating life after the war, Sybil makes the drastic decision to elope with Branson. However, Mary discovers her plan and, along with Edith and Anna, seeks them out and persuades Sybil to return and plead her cause openly to their parents.

As preparations are underway for Matthew and Lavinia's wedding, Lady Sybil's attempt to inform her parents of her wish to marry Branson is unsurprisingly met with shock and horror. Robert is violently opposed to the idea but his threats of social disgrace and disinheritance do not dissuade Sybil leading him to try buying off Branson but Branson's intentions are honourable and he refuses. Lady Grantham, Carson and Lavinia are taken ill by the Spanish flu. Thomas' black market venture was a spectacular failure, leaving him penniless and without a job but Carson's illness gives him a chance to become useful in the house. While Lavinia is resting upstairs, Matthew finds himself alone with Mary and tells her what Violet said to him: that he should marry her. Both of them acknowledge he could not as it would be terribly cruel to Lavinia. However, they then kiss just as Lavinia is coming down the stairs. When her illness delays the wedding, Lavinia tells Matthew that she heard and saw everything. She feels they should end their engagement but Matthew refuses. Fearing the outcome of Lavinia’s illness with regard to Matthew and Mary, Richard Carlisle comes to Downton. Daisy is distressed by William’s father’s request to visit him. Ethel is surprised to learn that Major Bryant’s parents want to see her but his father wants to take her child away permanently. Eventually she determines not to let him go as a mother's love is more important than a wealthy upbringing. Robert finds himself unable to control his desire for Jane, who willingly responds. However, their night-time encounter is interrupted and remains unconsummated; and Jane decides to leave. With the possibility of more trouble regarding Vera's death, Anna insists that she and Bates should marry that she may be able to support him through his difficulties as his wife. They marry in secret, with Lady Mary's permission and she arranges for them to spend their wedding night in a guest room. Cora becomes seriously ill and Clarkson fears the worst. O’Brien tirelessly cares for her and tries to ask for her forgiveness. However it is Lavinia who succumbs to the flu and dies saying that it is best for Matthew. Racked with guilt, Matthew tells Mary that any relationship between them is now impossible. Somewhat chastened by the recent events, Lord Grantham reluctantly gives his blessing to Sybil and Branson. The episode ends with Bates’ arrest for the murder of his wife.