The Babington Plot was a plan in 1586 to assassinate Queen Elizabeth I, a Protestant, and put Mary, Queen of Scots, her Roman Catholic cousin, on the English throne. It led to Mary's execution, a result of a letter sent by Mary (who had been imprisoned for 19 years since 1568 in England at the behest of Elizabeth) in which she consented to the assassination of Elizabeth.The long-term goal of the plot was the invasion of England by the Spanish forces of King Philip II and the Catholic League in France, leading to the restoration of the old religion. The plot was discovered by Elizabeth's spymaster Sir Francis Walsingham and used to entrap Mary for the purpose of removing her as a claimant to the English throne.

The chief conspirators were Anthony Babington and John Ballard. Babington, a young recusant, was recruited by Ballard, a Jesuit priest who hoped to rescue the Scottish Queen. Working for Walsingham were double agents Robert Poley and Gilbert Gifford, as well as Thomas Phelippes, a spy agent and cryptanalyst, and the puritan spy Maliverey Catilyn. The turbulent Catholic deacon Gifford had been in Walsingham's service since the end of 1585 or the beginning of 1586. Gifford obtained a letter of introduction to Queen Mary from a confidant and spy for her, Thomas Morgan. Walsingham then placed double agent Gifford and spy decipherer Phelippes inside Chartley Castle, where Queen Mary was imprisoned. Gifford organised the Walsingham plan to place Babington's and Queen Mary's encrypted communications into a beer barrel cork which were then intercepted by Phelippes, decoded and sent to Walsingham.On 7 July 1586, the only Babington letter that was sent to Mary was decoded by Phelippes. Mary responded in code on 17 July 1586 ordering the would-be rescuers to assassinate Queen Elizabeth. The response letter also included deciphered phrases indicating her desire to be rescued: "The affairs being thus prepared" and "I may suddenly be transported out of this place". At the Fotheringay trial in October 1586, Elizabeth's Lord High Treasurer Lord Burghley and Walsingham used the letter against Mary who refused to admit that she was guilty. But she was betrayed by her secretaries Nau and Curle who confessed under pressure that the letter was mainly truthful.

Mary, Queen of Scots (8 December 1542 – 8 February 1587), also known as Mary Stuart or Mary I of Scotland, was Queen of Scotland from 14 December 1542 until her forced abdication in 1567.

The only surviving legitimate child of James V of Scotland, Mary was six days old when her father died and she acceded to the throne. During her childhood, Scotland was governed by regents, first by the heir to the throne, James Hamilton, Earl of Arran, and then by her mother, Mary of Guise. In 1548, she was betrothed to Francis, the Dauphin of France, and was sent to be brought up in France, where she would be safe from invading English forces during the Rough Wooing. Mary married Francis in 1558, becoming queen consort of France from his accession in 1559 until his death in December 1560. Widowed, Mary returned to Scotland in August 1561. Following the Scottish Reformation, the tense religious and political climate that Mary encountered on her return to Scotland was further agitated by prominent Scots such as John Knox, who openly questioned whether her subjects had a duty to obey her. The early years of her personal rule were marked by pragmatism, tolerance, and moderation. She issued a proclamation accepting the religious settlement in Scotland as she had found it upon her return, retained advisers such as James Stewart, Earl of Moray, and William Maitland of Lethington, and governed as the Catholic monarch of a Protestant kingdom.

Mary married her half-cousin, Henry Stuart, Lord Darnley, in 1565, and in June 1566, they had a son, James. In February 1567, Darnley's residence was destroyed by an explosion, and he was found murdered in the garden. James Hepburn, 4th Earl of Bothwell, was generally believed to have orchestrated Darnley's death, but he was acquitted of the charge in April 1567, and the following month, he married Mary. Following an uprising against the couple, Mary was imprisoned in Loch Leven Castle. On 24 July 1567, she was forced to abdicate in favour of her one-year-old son. After an unsuccessful attempt to regain the throne, she fled southward seeking the protection of her first cousin once removed, Elizabeth I of England. (Elizabeth was the granddaughter of Henry VII of England, and Mary was his great-granddaughter.)

Mary had once claimed Elizabeth's throne as her own and was considered the legitimate sovereign of England by many English Catholics, including participants in a rebellion known as the Rising of the North. Perceiving Mary as a threat, Elizabeth had her confined in various castles and manor houses in the interior of England. After eighteen and a half years in captivity, Mary was found guilty of plotting to assassinate Elizabeth in 1586 and was beheaded the following year at Fotheringhay Castle. Mary's life, marriages, lineage, alleged involvement in plots against Elizabeth, and subsequent execution established her as a divisive and highly romanticised historical character, depicted in culture for centuries.