Scotland in the 11th century. Groups of witches gather in a wood beside a battlefield. The victorious generals Macbeth and Banquo enter. The witches hail Macbeth as Thane of Glamis, Thane of Cawdor, and king "hereafter." Banquo is greeted as the founder of a great line of future kings. The witches vanish, and messengers from the king appear naming Macbeth Thane of Cawdor.
At their castle, Lady Macbeth reads a letter from her husband telling of the encounter with the witches. She is determined to propel Macbeth to the throne (’Vieni! t’affretta!’). It is announced that King Duncan will stay in the castle that night and when Macbeth enters she urges him to take the opportunity to kill him. The King and the nobles arrive. Macbeth is emboldened to carry out the murder (’Mi si affaccia un pugnal?’), but afterwards is filled with horror. Lady Macbeth, disgusted at his cowardice, completes the crime, incriminating the sleeping guards by smearing them with Duncan’s blood and planting on them Macbeth’s dagger. The murder is discovered by Macduff. A chorus calls on God to avenge the killing (’Schiudi, inferno, . .’).
Macbeth is now king, but disturbed by the prophecy that Banquo, not him, will found a great royal line. To prevent this he tells his wife that he will have both Banquo and his son murdered as they come to a banquet. Lady Macbeth exults in the powers of darkness (’La luce langue’). Outside the castle a gang of murderers lie in wait. Banquo is apprehensive (’Come dal ciel precipita’). He is caught but enables his son Fleanzio to escape. In a hall in the castle, Macbeth receives the guests and Lady Macbeth sings a brindisi (’Si colmi il calice’). The assassination is reported to Macbeth, but when he returns to the table the ghost of Banco is sitting in his place. Macbeth raves at the ghost and the horrified guests believe he has gone mad. The banquet ends abruptly with their hurried, frightened departure.
The witches gather around a cauldron in a dark cave. Macbeth enters and they conjure up three apparitions for him. The first advises him to beware of Macduff. The second tells him that he cannot be harmed by a man ’born of woman’. The third that he cannot be conquered till Birnam Wood marches against him. Macbeth is then shown the ghost of Banquo and his descendants, eight future Kings of Scotland, verifying the original prophecy. He collapses and regains consciousness in the castle. Macbeth and his wife resolve to extirpate the families of Macduff and Banquo (’Ora di morte e di vendetta’).
A chorus of Scottish refugees (’Patria oppressa’) stand near the English border. In the distance lies Birnam Wood. Macduff is determined to avenge the deaths of his wife and children at the hands of the tyrant (’Ah la paterna mano’). He is joined by Malcolm, the son of King Duncan, and the English army. Malcolm orders each soldier to cut a branch from a tree in Birnam Wood and carry it as they attack Macbeth’s army. They are determined to liberate Scotland from tyranny (’La patria tradita’).
In Macbeth’s castle a doctor and a servant observe the Queen as she walks in her sleep, wringing her hands and attempting to clean them of blood (’Una macchia’). Macbeth has learned that an army is advancing against him but is reassured by remembering the words of the apparitions. (’Pietа, rispetto amore’) He receives the news of the Queen’s death with indifference. Rallying his troops he learns that Birnam Wood has indeed come to his castle. Battle is joined. Macduff pursues and kills Macbeth, telling him that he was not ’born’ of woman but ’cut’ from his mother’s womb. The opera ends with a hymn to victory sung by bards, soldiers, and Scottish women.