The new legal heirs to Downton, lawyer Matthew Crawley and his nurse mother Isobel are invited to live on the estate, but there is resentment of them as interlopers from both up and downstairs as interlopers.

Mrs. Hughes is reunited with an old beau, now a widower proposing marriage, and the Countess hires Matthew Crawley to see if the will can be broken and disagrees with his mother on a diagnosis.

Mary finds it was Edith who let the ambassador know about Pamuk's death, Cora announces her pregnancy, and Thomas and O'Brien hatch new slanders against Bates as War clouds loom.

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 John 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 nearly succumbs to a kiss from the married farmer Mr. Drake. Sybil and Thomas work in the cottage hospital, where the latter begins to learn some humanity. At Isobel's suggestion - and to Violet's dismay - Downton Abbey is turned into a convalescent ward to ease the hospital's bed shortage. Mary invites middle-aged newspaper tycoon, and prospective beau, Sir Richard Carlisle to a dinner party, also attended by the Crawleys and Lavinia. Suspicious of Carlisle, Violet invites her daughter and sister to the Earl, Lady Rosamund, who is intrigued by the fact that Carlisle and Lavinia already seem well-acquainted. Carson, despite being taken ill whilst serving dinner, is still perceptive enough to suggest to Mary that Matthew is really the man for her.

Downton is turned into a convalescent hospital for the war wounded and through circumstances Thomas is given authority in its operation as Anna and Bates are briefly reunited and Branson plots against a heroic general 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 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.

Ethel confronts her baby's grandparents, Bates thinks he might have played a role in his wife's death, Branson and Sybil elope, and Carlyle 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.

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.

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?

An unofficial will from Matthew comes into the family's hand, Thomas plots against Anna, Rose gets involved in a scrap at a servant's dance, and Mrs. Crawley tries to reconcile Carson and Trigg.

An extravagant house party at the Abbey gives the Crawleys a chance to reconnect with old friends, but some guests prove more welcome than others, and along with the celebrations come deceit and heartache.

Anthony Gillingham returns to Downton to propose to Mary, Edna tries to coerce Tom into marrying her, and Anna will not tell Bates what's bothering her.

Mrs. Hughes tells Bates an edited version of Anna's rape, Edith goes to London to see Michael, Alfred takes a culinary test, and the Countess suspects new employee Pegg of theft and Robert tries to keep a tenant.

A birthday party is planned for Robert, but Rose's contribution to the event surprises those above and below stairs, a new farming venture on the Downton estate comes with dramatic repercussions for Mary, and Edith receives troubling news.

Cora's playboy brother, Harold, is in trouble, so Robert must travel to America to help bail him out; a new farming venture at Downton sees Blake and Mary putting aside their differences.

Tim Drewe guesses the parentage of Marigold, Mary receives another proposal from Tony, Violet plays matchmaker, Thomas continues to press Baxter for information with blackmail, and a flash fire threatens the mansion.

James leaves Downton, Mary has a weekend rendezvous with Gillingham, Carson and the Earl disagree for the site of the War memorial, a wireless becomes part of Downton life, and Edith becomes Marigold's godmother.

Tom ends his relationship with Sarah, Rose meets a young man of Russian descent, Rosamund's visit to Marigold has consequences, Mrs. Patmore asks advice for her inheritance, and Simon Bricker expresses his love for Cora.

Violet's new maid doesn't seem to be working out, Kuragin reveals he still loves Violet, Anna realizes Bates' innocence, and Thomas reveals a secret to Baxter.

Kuragin tells Violet he wants to live with her, someone tries to break up the Atticus Rose wedding, Daisy wants to live in London, and Anna is accused of Green's murder.

Lady Mary's past catches up with her when an unwelcome visitor delivers an ultimatum, and news about the running of Downton Hospital puts Violet on the warpath.

What begins as a happy day out for the family and servants ends in panic and leaves Robert with a difficult decision to make.

An old acquaintance comes to Edith's aid, while Mr Carson and Mrs Hughes' big day brings an unexpected arrival.

Violet embroils the Minister of Health in the hospital row, but his visit ends in catastrophe. Mary's suspicions are aroused.

Downton Abbey opens its doors to the public for charity, Barrow's actions are misconstrued, Mary and Henry's romance blossoms, and tensions between Cora and Violet reach a dramatic climax.

Mary endeavors to build bridges with her sister while Edith's secret continues to pose a threat. As Henry settles into the role of husband and stepfather, finding his place at Downton proves more difficult.