The first act of the play opens amidst thunder and lightning with the Three Witches deciding that their next meeting shall be with Macbeth. In the following scene, a wounded sergeant reports to King Duncan of Scotland that his generals Macbeth, who is the Thane of Glamis, and Banquo have just defeated the allied forces of Norway and Ireland, who were led by the traitor Macdonwald. Macbeth, the King's kinsman, is praised for his bravery and fighting prowess.
The scene changes. Macbeth and Banquo enter, discussing the weather and their victory ("So foul and fair a day I have not seen"). As they wander onto a heath, the Three Witches enter, who have waited to greet them with prophecies. Even though Banquo challenges them first, they address Macbeth. The first witch hails Macbeth as "Thane of Glamis", the second as "Thane of Cawdor", and the third proclaims that he shall "be King hereafter." Macbeth appears to be stunned to silence, so again Banquo challenges them. The witches inform Banquo that he will father a line of kings, though he himself will not be one. While the two men wonder at these pronouncements, the witches vanish, and another thane, Ross, a messenger from the King, arrives and informs Macbeth of his newly bestowed title: Thane of Cawdor. The first prophecy is thus fulfilled. Immediately, Macbeth begins to harbour ambitions of becoming king.
Macbeth writes to his wife about the witches' prophecies. When Duncan decides to stay at the Macbeths' castle at Inverness, Lady Macbeth hatches a plan to murder him and secure the throne for her husband. Although Macbeth raises concerns about the regicide, Lady Macbeth eventually persuades him, by challenging his manhood, to follow her plan.
On the night of the king's visit, Macbeth kills Duncan. The deed is not seen by the audience, but it leaves Macbeth so shaken that Lady Macbeth has to take charge. In accordance with her plan, she frames Duncan's sleeping servants for the murder by planting bloody daggers on them. Early the next morning, Lennox, a Scottish nobleman, and Macduff, the loyal Thane of Fife, arrive. A porter opens the gate and Macbeth leads them to the king's chamber, where Macduff discovers Duncan's corpse. In a feigned fit of anger, Macbeth murders the guards before they can protest their innocence. Macduff is immediately suspicious of Macbeth, but does not reveal his suspicions publicly. Fearing for their lives, Duncan's sons flee, Malcolm to England and Donalbain to Ireland. The rightful heirs' flight makes them suspects and Macbeth assumes the throne as the new King of Scotland as a kinsman of the dead king.
Thodore Chassriau (18191856), Macbeth seeing the Ghost of Banquo, 1854.
Despite his success, Macbeth remains uneasy about the prophecy about Banquo, so Macbeth invites him to a royal banquet where he discovers that Banquo and his young son, Fleance, will be riding out that night. He hires two men to kill them, while a third murderer also appears in the park before the murder. While the assassins kill Banquo, Fleance escapes. At the banquet, Banquo's ghost enters and sits in Macbeth's place. Only Macbeth can see the spectre; the rest panic at the sight of Macbeth raging at an empty chair, until a desperate Lady Macbeth orders them to leave, claiming that her husband is merely afflicted with a familiar and harmless malady.