King Duncan has learnt about the defeat of Macdonwald from an injured sergeant. The Thane of Ross also informs him that the Thane of Cawdor is a traitor and his been captured. Scotland has won the war. Duncan is very happy with Macbeth and names him the new Thane of Cawdor.
Macbeth and Banquo are on their way back to Forres when they come across the three witches. The witches tell Macbeth that he will become the Thane of Cowder and the king after. They also tell Banquo that his children will be kings although he will not be one. The witches disappear.
The execution of the Thane of Cawdor is over. The King holds a court and Macbeth, Banquo, Ross, Malcom and Angus are present. The King announces he will be staying at Macbeth's castle on the way home. He also names Malcom his successor.
A messenger comes to Lady Macbeth to tell her that the king himself is coming to stay a night.
Scene 5: Lady Macbeth has received Macbeth's letter informing her of the witches prophecies. She fears that Macbeth is too kind to kill Duncan and she wants to help him.
Macbeth is debating committing murder when Lady Macbeth walks in and tries to convince him. She tells him he will be a coward in her eyes if he does not kill Duncan. Macbeth agrees to her plan.