After Bates' mother dies, he hopes his inheritance will buy him a divorce and allow him to marry Anna, Matthew announces his engagement to Lavinia Swire, and Sybil gets involved in the war effort.
April 1917. With Bates still absent, Isobel's butler Molesley makes a play for Anna but is rejected. Robert gets a new valet, shell-shocked ex-soldier Henry Lang, whilst William goes off to war. Edith learns to drive a tractor extremely well, and succumbs to a kiss from the married farmer Mr. Drake.
Downton is turned into a convalescent hospital for the war-wounded and, through circumstances, Thomas is given authority in its operation. Anna and Bates are briefly reunited, and Branson plots against a heroic general who is dining at Downton.
Matthew and William are missing in France, the mounting tensions between Cora and Isobel result in Isobel's volunteering for France, Bates returns to Downton, and the servants open a soup kitchen for unemployed veterans.
August 1918: Deserted by the baby's father, Ethel has been installed with her child in a cottage on the estate by a sympathetic Mrs. Hughes, who brings her food. Jane, a war widow, has taken Ethel's place as a maid. Vera Bates returns, having spent John's money.
An unrecognizable burn victim turns up at the convalescent home claiming to be Mary's presumed drowned cousin Patrick, Carlisle plans to lure Carson from Downton.
Ethel confronts her baby's grandparents, Bates thinks he might have played a role in his wife's death, Branson and Sybil try to elope, and Carlisle tries to recruit Anna to spy on Mary.
The Spanish Flu disrupts plans for Matthew's wedding when Cora, Lavinia, Carson, Molesley, and other staff members fall ill. Ethel has to decide the future for her son, and Jane resigns from Downton.
Christmas 1919. Downton Abbey is hosting a lavish Christmas party, yet despite being the season of goodwill, tensions are rife and Bates' arrest has cast a shadow over the festivities.
