The film begins with an elderly Lady Thatcher buying milk unrecognized by other customers and walking back from the shop alone. Over the course of three days we see her struggle with dementia and with the lack of power that comes with old age, whilst looking back on defining moments of her personal and professional life, on which she reminisces with her (dead) husband, Denis. She is shown as having difficulty distinguishing between the past and present. A theme throughout the film is the personal price which Thatcher has paid for power. Denis is portrayed as somewhat ambivalent about his wife’s rise to power, her son Mark lives in South Africa in the present day and is shown as having little contact with his mother, whilst it is suggested that Thatcher had a strained relationship both with her own mother and with her daughter Carol.
In flashback we are shown Thatcher’s youth working in her father’s grocery store in Grantham, listening to his political speeches as Alderman, and her struggle as a lower middle-class young woman trying to break into the male-dominated Tory party and find a seat in the House of Commons. Her marriage to wealthy businessman Denis Thatcher, and her struggle to fit in as a “Lady Member” of the House, and of Edward Heath’s cabinet are also shown, as is her friendship with Airey Neave (later assassinated by the Irish National Liberation Army), her decision to stand for Leader of the Conservative Party, and her voice coaching and image change.
Further flashbacks examine historical events during her time as Prime Minister of the United Kingdom including the rising unemployment due to her monetarist policies and the tight 1981 budget (over the misgivings of “wet” members of her Cabinet – Ian Gilmour, Francis Pym, Michael Heseltine and Jim Prior), the Brixton Riots of 1981, the miners’ strike of 1984-5, and the bombing of the Grand Hotel (Brighton) during the 1984 Conservative Party Conference, at which she and Denis were almost killed. We also see (slightly out of chronological sequence) her decision to retake the Falkland Islandsfollowing their invasion in 1982, the sinking of the ARA General Belgrano and subsequent victory in the Falklands War, her friendship with Ronald Reagan, and the economic boom of the late 1980s.
By 1990 Thatcher is shown as an imperious but ageing figure, ranting aggressively at her Cabinet, refusing to accept that the Community Charge (the “Poll Tax”) is regarded as unjust, and fiercely opposed to European Integration. Her deputy Geoffrey Howe resigns after being humiliated by her in a Cabinet meeting, Michael Heseltine challenges her for the party leadership and her Cabinet colleagues force her resignation as Prime Minister, about which she is still angry and bitter twenty years later.
Eventually, Margaret is shown finally packing up her late husband’s belongings, and telling him it’s his time to go. Denis finally leaves her (without his shoes), and having dealt with her grief properly, she is left alone washing up a teacup in her kitchen – something she had promised Denis she would never do.