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.