Lord Robert Crawley and his family live a life of leisure, while a fleet of servants, including butler Carson, attend to their every need. But two events conspire to shake things up: the sinking of the Titanic, which claims Crawley's heirs, and the return of his valet, Bates. Since Crawley and Lady Cora have three daughters, his distant solicitor cousin, Matthew, becomes heir to the estate. With that, the scheming begins, since Thomas the footman views Bates as an interloper and Crawley's mother, Violet, feels the same way about Matthew's mother, Isobel.
April 1912:- The heir to the title of Earl of Grantham,long time inhabitants of Downton Abbey,perishes on the 'Titanic'. Robert,the benevolent current earl,owes his wealth to his American wife Cora but they have only three daughters,who cannot inherit by law,so another heir must be found by marrying off Mary,the eldest girl. The Duke of Crowborough is a possibility but he is a closet gay who only has eyes for Thomas,the handsome but obnoxious footman,and soon departs. Robert's mother,the dowager,and Cora decide that the next best candidate is Matthew Crawley,a distant cousin,but Cora knows that the spirited Mary will not be happy with their choice. Downstairs there is also unrest as Thomas is passed over for promotion to valet in favour of Robert's batman from the Boer War,John Bates,who now limps due to a war wound. Along with Cora's maid Miss O'Brien, Thomas schemes to discredit Bates in the eyes of butler Carson and forces his resignation but Robert intervenes and keeps him on.Thomas vents his anger on second footman William but he has an ally in the sensible housekeeper Mrs. Hughes.
September 1912. Designated heir Matthew Crawley and his mother Isobel arrive and move into a house in the grounds of Downton Abbey but Matthew is uncomfortable with having servants and is not keen on an arranged marriage - something he has in common with Lady Mary. Robert's mother Violet looks down on them as they are not from her class - Matthew is a working solicitor and Isobel,a trained nurse and doctor's widow,who nonetheless impresses when she helps at the local hospital and saves the life of one of Robert's tenants. Cora upbraids the two nastiest servants,O'Brien and Thomas,for sneering at the Crawleys but impresses upon Mary the financial need for the marriage. Carson is blackmailed by Grigg, a man with whom he once had a music-hall act but Robert takes his part and sees Grigg off. Whilst Carson feels foolish for having a less than aristocratic past he is supported by Bates and the two men become friends
March 1913. Gwen,one of the maids,has bought a typewriter and has applied for a secretarial post. Most of the staff are dismissive of her aspirations but the family - except Violet of course - are supportive and youngest daughter Sybil offers to supply a reference. Evelyn Napier,considered an eligible catch for Mary, arrives for the hunt,bringing his handsome friend Kemal Pamuk,a Turkish diplomat,who throws himself at her. He goes to her room at night for sex,during which he dies of a heart attack. Mary,Cora and head housemaid Anna return the body to his room and agree to say nothing but are seen by Daisy the kitchen maid. The gruesome twosome of O'Brien and Thomas are also suspicious. Matthew spends a delightful day with Edith,the youngest daughter,whilst Mrs. Hughes literally helps Bates out of a painful situation and they become friendly.
May 1913. A fair comes to the village and here Mrs. Hughes meets up with an old flame,Joe,who once asked her to marry him and does so again but once more she refuses. Despite being gay Thomas escorts Daisy to the fair purely out of spite as he knows William is fond of her. The gesture is not lost on either John Bates or Mrs. Hughes. Gwen is not called for interview for the secretarial post but Sybil agrees to support future applications. A new chauffeur, Tom Branson, arrives. He is well-read and politically aware. Having got one over on Isobel regarding a medical diagnosis,Violet attempts to talk Robert out of a need for an arranged marriage but fails. Mary,seeing herself as no more than a commodity,unburdens herself to Matthew and they get a little closer.
August 1913. O'Brien and Thomas continue to spread their malice,ensuring that Lady Edith learns from Daisy where Kemal died and attempting to frame John Bates for the theft of a snuff-box though Anna,clearly fond of John,ensures the plan backfires on them. Thomas's gossip also discredits Lady Mary's eligibility as a bride and the family must entertain the middle-aged Sir Anthony Strallen as a prospective husband. Mary is bored by him and it brings her closer to Matthew but Edith seems genuinely interested in him. Mrs. Patmore,the cook,must accept that her eye-sight is failing and Lady Sybil continues to encourage Gwen in her secretarial applications whilst Isobel actually teaches Lady Violet some altruism at the annual produce show.
May 1914. Encouraged by politically aware chauffeur Tom Branson, the socially conscious Lady Sybil espouses politics as a means of aiding equality for women and the lower classes, to her father's anger. At a political meeting she is injured in a scuffle and rescued by Matthew. A grateful Lady Mary accepts Matthew's proposal of marriage but tells her mother she feels she should come clean about Kemal to him. Rumours about this indiscretion are now rife and Cora tells her mother-in-law how she helped Mary move the body. Edith continues to see more and more of Sir Anthony whilst O'Brien and Thomas continue to persecute John. They tell Carson they saw him steal wine and get Daisy to support them. However Daisy does the decent thing and admits she was put up to it. Bizarrely, John, though he knows Thomas to be the wine thief, offers no explanation, confessing to being a former alcoholic and offering his resignation.
July 1914. In London former suitor Evelyn Napier assures Lady Mary that it was Edith, not he,who spread gossip about her and Kemal. Mary counters by wrecking her sister's marriage plans with Sir Anthony. Robert is reluctant to dismiss John even though O'Brien and Thomas have obtained a letter claiming that he stole from a previous employer. Anna accompanies Mrs. Patmore to London for eye tests,resulting in corrective surgery and whilst there,discovers that John took the blame for the theft for his ex-wife Vera, a fact which Robert is pleased to hear. Thomas, fed up at his failure to get John sacked,and sensing war on the way,joins the Army Medical Corps whilst Sybil finally gets Gwen her secretarial post. Cora is pregnant, a fact which puts the proposed marriage between Mary and Matthew in doubt, should the baby be a son and heir. However,thanks to O'Brien leaving a bar of soap on the floor, Cora slips and miscarries. All the staff except O'Brien cheer William on as he beats Thomas up for his unfeeling remarks on the loss. Matthew nonetheless feels that the engagement was only an act of pragmatism likely to be altered if an heir had been born and decides to leave Downton Abbey. But everybody's news is overshadowed as they hear that,as expected,Britain is at war with Germany.