Spring of 1920. Wedding guests descend on Downton Abbey, where disasters threaten. One of which is Cora's freewheeling American mother, who tries to loosen up her in-laws.

A conflict between two members of the house staff escalates. Meanwhile, the family tries to impress Martha by planning a lavish dinner party.

The fate of Downton Abbey hinges on a letter from a dead man. Edith and Sir Anthony face their own fateful moment. Mrs. Hughes confronts a crisis.

August 1920: Two social revolutions arrive at Downton Abbey: the Irish civil war and the fight for women's suffrage. A mysterious conspiracy keeps Anna and Bates apart.

The Crawleys excitedly await as the new addition to the family is soon to come. Meanwhile, Anna attempts to uncover evidence for Bates's innocence. But then, when tragedy strikes, will things ever be the same again?

Things go badly amiss at Downton Abbey. Robert and Cora are not speaking. The servants are shunning Matthew's mother, Isobel. And Matthew and Robert have fallen out. Bates takes a gamble.

Change arrives in a big way for several key characters at Downton Abbey. A yearly cricket match with the village sees old scores settled and new plots are hatched.

The Crawleys go to Duneagle Castle to celebrate Christmas with the MacClares. Everyone is delighted as they fish, hunt, and dine. Unfortunately, when the Crawleys return, tragedy strikes. Will things ever be the same again?