Elizabeth I, queen of England, is considering a politically advantageous marriage to the French king, despite her secret love for the Earl of Leicester.
Although the people demand clemency for Mary Stuart, Cecil, Elizabeth’s treasurer, insists on the executioner’s axe. When the Earl of Leicester appears, Elizabeth asks him to deliver her acceptance to the French ambassador, hoping in vain that Leicester will be outraged at the idea of her marriage to someone else.
Talbot, the Earl of Shrewsbury, privately delivers a portrait and a letter from Mary Stuart to Leicester, who sees her “beloved smile” and vows to free her.
Elizabeth’s suspicions are aroused; jealous of Mary Stuart, she demands that Leicester explain himself. He manages to talk his way out of the situation, but gives Elizabeth a letter from Mary Stuart asking to see her. Leicester urges the queen to visit Mary Stuart in her prison.
In the garden of Fotheringhay Castle, Mary Stuart confesses to her nurse Anna that she is dreading her meeting with Elizabeth, since she cannot control her emotions. Leicester appears, assures Mary Stuart of his love and his loyalty, and urges her to believe that her meeting with Elizabeth will set her free.
Elizabeth arrives accompanied by Cecil, who continues to call for Mary Stuart’s head, and Leicester, who pleads her case – which, however, only turns Elizabeth against Mary Stuart: “I hate her! He thinks only of her!” Mary, accompanied by Talbot and Anna, kneels before Elizabeth, and asks for her forgiveness. Angrily, Elizabeth tells her she is a despicable and wretched criminal. Leicester pleads with Mary Stuart to remain strong, reminding her of his love. Mary, however, becomes more and more infuriated, finally insulting Elizabeth by calling her a “revolting bastard.” Elizabeth calls for the guards and tells her she will be put to death.
Cecil pressures Elizabeth to sign Mary Stuart’s death sentence. She finally signs it; Leicester enters and pleads for clemency. Elizabeth reacts angrily and orders Leicester to witness the execution.
Cecil brings Mary her death warrant. Once she is alone with Talbot, Mary asks him to free her soul. Talbot takes off his coat, revealing the vestments of a priest, and hears Mary’s confession. She confesses to being guilty of her husband’s death and to a later relationship with his alleged murderer. Then she proclaims her innocence of the crimes for which she is being executed.
Mary prays as she arrives for the execution, accompanied by her confidant. Her last prayer is for Elizabeth, whom she blesses and forgives. Leicester enters and curses Mary’s enemies as unworthy. Mary asks him to walk with her to the executioner and goes to her death as her followers grieve.