Set in April 1912. Lord Grantham’s cousin, James Crawley, who is Lord Grantham's heir presumptive, and his son, Patrick Crawley, both die in the sinking of the RMS Titanic. With no male offspring, speculation mounts as to who will become his heir. Lord Grantham hires Bates to be his valet.
As Daisy the kitchenmaid opens up the house a telegram is delivered. It is 16th April 1912 and the Titanic has gone down, taking with it Lord Grantham’s heir, James Crawley, and his son, Patrick. So who is the new heir? Not just to the earldom but to Downton Abbey, itself, which is entailed to the title. Violet, the Dowager Countess, assumes Robert, the present Earl, will break the entail and make an heiress of his eldest daughter, Mary, but Robert is not so sure. To make matters worse, his wife, Cora, has her own money tied up in the estate, and there is no way to extract it without crippling Downton. Even if Robert could break the entail, or take Cora’s money out of it, would he want to?
Below stairs, a new valet, John Bates, arrives. Bates was Robert’s batman during the Boer War and Robert welcomes him. However, he looks as shocked as the rest of the servants when he sees Bates’s limp. Will this hamper his duties? Cora’s maid, O’Brien, and first footman, Thomas, who wanted Bates’s job, deliberately try to sabotage his first days at work.
Mary was supposed to marry the heir, the late Patrick Crawley, but his death has freed her to move on. She believes her own prospects have changed for the better, and now she angles to catch the young Duke of Crowborough. Her sister, Edith, was in love with Patrick and seethes with resentment towards Mary. The Duke arrives at Downton, ostensibly to present his condolences, but after dinner he requests an interview with Robert, presumably to ask for Mary’s hand.
But when he learns that Robert is not intending to challenge the entail he withdraws his offer, without ever in fact making it. It was Thomas who brought the Duke to Downton, luring him with the prospect of the Grantham money. He and Thomas shared a summer dalliance and Thomas intends to use this to further his own career, blackmailing the Duke with his own letters if he has to. However, the Duke is one step ahead of Thomas who can only watch as the incriminating pages go up in flames.
Meanwhile, Robert informs Bates that his disability is interfering with his work and he will have to go. Bates seems to take the news well, but the Head Housemaid, Anna, hears him crying in his room. However, as Crowborough leaves Robert finds himself unable to let Bates down in this way, and to the amazement of Cora and the servants he asks the valet to stay.
Mary’s fury is matched by Cora’s surprise when they realise Robert has made up his mind and will not challenge the entail. He has discovered the identity of his new heir, a distant cousin, and intends to write to the young man and invite him to Downton.