A chronicle of the lives of the British aristocratic Crawley family and their servants in the early twentieth century.

Lord Robert Crawley, Earl of Grantham (Hugh Bonneville) sees his family heritage, especially the grand country home Downton Abbey, as his mission in life. The death of his heir aboard R.M.S. Titanic means distant cousin Matthew Crawley (Dan Stevens), a Manchester lawyer, suddenly is next in line and accepts moving onto the vast estate with his even more modernist, socially engaged mother, who clashes with his Lordship's domineering, conservative mother, the dowager countess.

Marrying off the daughters is another concern. Meanwhile, the butler presides over a staff which serves the family, but also lead most of their entire lives in the servants' quarters, intriguing amongst themselves.