On a barren heath, witches predict the future of Macbeth and his companion Banquo. The witches declare that Macbeth will first become Thane of Cawdor, then King of Scotland, and that Banquo's descendants will be kings of Scotland. Almost immediately, messengers proclaim that Macbeth has been named Thane of Cawdor, upon the recent execution of the previous thane. Macbeth is greatly struck by this partial fulfillment of the prophecy and wonders if the rest will come true as well.
At Macbeth's castle, Lady Macbeth ponders a letter she has received from her husband telling her of the witches' prophecy and its aftermath. She determines that Macbeth must take decisive steps to fulfill all the prophecies and seize power at any price, but she fears that her husband will falter at the crucial moment. She resolves to infuse him with her own courage, and when he arrives moments later, she persuades him to murder Duncan, King of Scotland, who is spending the night with them, and to blame the killing on Duncan's guards. Macbeth carries out their plan despite his horror of the deed. Macduff, a Scottish nobleman, arrives with Banquo, and they find the body of the king. Duncan's son Malcolm flees to England.
With Malcolm out of the way, Macbeth is crowned king, but he fears that, in fulfillment of the prophecy, the crown will pass to Banquo's line. To prevent this, he arranges the murders of Banquo and his son Fleance. Macbeth's assassins succeed in killing Banquo, but Fleance escapes.
At a banquet, Macbeth sees Banquo's ghost. Macbeth's distraught behavior frightens his guests despite Lady Macbeth's attempts to defuse the situation. Macduff grows suspicious and resolves to flee the country.
Macbeth revisits the witches to hear further prophecies. Apparitions warn him to beware of Macduff; they also assure him that no man born of woman can harm him and, furthermore, that his power is secure until Birnam Wood rises up against him. The witches, however, reaffirm that Banquo's descendants are destined to rule Scotland. Musing with Lady Macbeth over these predictions, Macbeth decides to kill Macduff and his whole family.
Macduff has joined forces with Malcolm, who is leading an army against Macbeth. Encamped in Birnam Wood, Macduff mourns the loss of his wife and children, murdered by Macbeth, and vows vengeance. Malcolm orders his soldiers to camouflage their approach to Macbeth's castle by plucking branches to hide behind as they march.
Lady Macbeth, plagued by a guilty conscience, walks in her sleep, observed by her lady-in-waiting and a doctor. She vainly attempts to wash off the blood she sees on her hands.
Macbeth, preparing for battle against Malcolm's forces, reflects bitterly on the barrenness of his own life, realizing that his crimes have placed him beyond the reach of human sympathy and love. Cries from within the castle alert him to the death of Lady Macbeth, to which he reacts with indifference. Messengers bring the news that Birnam Wood is moving toward the castle; Macbeth, though shaken, prepares to fight. Macduff finds and fights Macbeth. Revealing that he was not born of a woman but rather ripped from his mother's womb, Macduff kills Macbeth. Malcolm is declared king.