The family and staff of Downton are shocked when they find that the heir to the title and fiancé of the Earl's daughter Mary perished on the Titanic, and the Earl hires a crippled army comrade as valet.

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.

Gwen's ambitions to leave service to become a secretary is discouraged, Bates takes painful steps to overcome his limp, and a dashing Turkish diplomat visiting Downton seems to work his charms on everyone - especially Mary.

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.

Bates sees Thomas stealing a bottle of wine, the footman tries to frame him for petty theft, and Mrs. Crawley tries to convince the Dowager Countess to surrender her annual entitlement prize for best bloom in the village.

O'Brien and Thomas continue their efforts to frame Bates, Mary falls in love with Matthew, and Sybil is injured in a political disturbance and Branson is blamed.

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.

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.

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.

A vindictive Ms. O'Brien hatches a damaging plot. Edith makes a major decision. Matthew devises 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.

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?

Mary is still inconsolable six months after Matthew's death, Edith supports Michael going to Germany to divorce his wife, Molesley looks for a job, and there is a surprise applicant for Ms. O'Brien's job.

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.

Rosamund comes up with a plan to help Edith, but Violet sees right through it; Isobel is the object of someone's attention, while Mary asks Gillingham for a very big favor.

Summer of 1923. It's summer and as part of Rose's 'coming out' she is to be presented at Buckingham Palace. The Crawley family go to London to prepare Grantham House for this busy social program.

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.

Mary wakes up in bed with Tony Gillingham after their tryst and returns to Downton, where she learns that a building firm want to buy land for a housing estate, to which Robert objects. Violet discovers from her butler Spratt about Mary and Tony but covers for her before summoning her for an explanation. Mary explains to her that she plans to marry Tony but later tells Tom the truth, that she has no intention. In return he confesses that he is considering a move to America. Following the policeman's visit, Anna is perturbed that her ordeal will be revealed, particularly as the animosity between John and Green comes to light. John gives his alibi, that he spent the day in question in York, and Mrs Hughes and Mary agree to collude with this. As Barrow goes to visit his dying father, Baxter tells Cora that she was beguiled into the jewel theft by a cruel footman called Peter Coyle, whom she loved but who fled leaving her to take the blame. Tim's wife wants to bar Edith from seeing Marigold, whilst Rose hosts a benefit for a group of Russian political exiles and Violet is taken aback by one of their number.

The Countess confesses her past with Prince Kuragin, Lord Merton proposes to Isobel, Rose's parents are divorcing, Lord Grantham becomes jealous of Simon, and Lady Mary tells Gillingham she won't marry him.

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.

Atticus brings his parents, Edith and her daughter are brought home by Cora, Tom decides to take his daughter to America, Baxter volunteers to testify for Bates, and Isis is dying.

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.

Autumn of 1924. It's grouse shooting season and Rose's father-in-law invites the Crawley family to a shooting party in Northumberland.

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.

Anna and Mary face a crisis and a figure from the past surprises those above and below stairs.

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.

The family face a shocking turn of events at Brooklands racetrack while Molesley and Daisy are put to the test.

Romance blossoms but a betrayal of trust threatens the chance of lasting happiness. Thomas considers desperate measures.

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.

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.

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

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

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

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.

The family face a shocking turn of events at Brooklands racetrack while Molesley and Daisy are put to the test.

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.

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.

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.

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.