The Court awaits the arrival of Queen Elizabeth, who is expected to announce her marriage to the Duke of Anjou. Elizabeth reveals that she is still undecided on whether or not to unite the thrones of England and France by this marriage, but assures her Court that she will only act for the good of the people. Aside, she confesses her secret love for Robert Dudley, Earl of Leicester. Talbot and the courtiers then plead for mercy towards Mary Stuart, Queen of Scots, imprisoned at Fotheringhay, but Elizabeth is unwilling to relent, a course in which she is encouraged by Sir William Cecil. Leicester arrives and is ordered by Elizabeth to take her ring to the French envoy as a token of her provisional acceptance of the marriage proposal. Deeply hurt by his cool reaction to this news, the Queen departs. Talbot tells Leicester of a meeting with Mary and gives him a portrait of her, along with a letter begging for his help. Leicester vows to secure Mary's freedom. When Elizabeth returns she demands to see the letter he is holding. Despite her anger at Mary's aspirations to the English crown and her intense jealousy of Leicester's affections, she reluctantly agrees to visit her.
Mary and her companion, Hannah, recollect their early life in France. Hearing the sounds of the Royal Hunt, Mary realizes that Elizabeth is in the vicinity. Leicester arrives and explains that the Hunt is only a pretext for Elizabeth to visit Mary and persuades her to be submissive if she hopes for mercy. As the two women meet for the first time, each feels instant hostility towards the other. Mary humbles herself but Elizabeth responds by accusing her of treachery, murder and debauchery. Mary, taunted beyond endurance, denounces Elizabeth as the unlawful daughter of Anne Boleyn. Cecil urges Elizabeth to sign the order for Mary's execution, following her complicity in the Babington plot to assassinate the Queen, but Elizabeth is still undecided; she cannot bring herself to condemn an anointed monarch. Cecil eventually succeeds in persuading Elizabeth to sign the warrant.
When Leicester learns that Mary has been condemned to death he makes a final plea for her life, upbraiding Elizabeth for her cruelty when she refuses to yield. He is then detailed by the Queen to witness Mary's execution. Mary is visited by Talbot and Cecil; the latter hands her the death sentence and leaves her alone with Talbot. He tells her of Elizabeth's decision that Leicester is to witness her execution. Mary becomes distraught and imagines that she sees the ghosts of her former husband and lover, Darnley and Rizzio. Talbot urges her to place her trust in Heaven and to prepare to face her death with resignation.
A waiting crowd watches the preparations for Mary's execution. Mary bids them farewell and they join her in a final prayer for heavenly pardon. Mary forgives Elizabeth and prays for the welfare of England. She breaks down when Leicester arrives, protesting her innocence and asking him to support her as the hour of her death approaches. A final cannon shot is heard and Mary is led out to the scaffold.
