Wedding guests descend on Downton Abbey, where disasters - large and small - threaten. One is Cora's freewheeling American mother, who tries to loosen up her in-laws.
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 Crawley family faces its severest test yet. Meanwhile, new faces try to fit into the tight-knit circle of servants. New evidence turns up in a baffling case.
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.
A vindictive Ms. O'Brien hatches a damaging plot. Edith make a major decision. Matthew has a major plan for changing things, and Tom's brother pays a visit.
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.