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.

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 but with no intention of sticking to their arrangement and planning to make money by selling the story of Lady Mary's indiscretion to Carlisle's newspaper. Tipped off by Anna, Mary goes to see him and explains all, thus scotching Vera's plan as the newspaper owner threatens her with libel action. Having returned to the war, both Matthew and William sustain severe injuries at the Battle of Amiens, fatally in the case of William, who marries Daisy. Mary is glad to become a hospital auxiliary to nurse Matthew, though his spinal damage will, in all probability, leave him paralysed from the waist down and impotent.

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, and Bates' wife reneges on her divorce agreement.