Having heard the predictions of the three bearded sisters, Macbeth finds himself enmeshed in another dimension where "nothing is what is not." Yet, convinced that fate intends for him to be king, Macbeth, along with an encouraging and cupidinous Lady Macbeth, decide to accelerate this determined path upon which Macbeth seems headed.
To fulfill the witches' prophesy that Macbeth will be king, they must first kill King Duncan. And, in order to embolder Macbeth, Lady Macbeth calls upon the preternatural world to unsex herself so that she can provide her husband with the strength to carry out regicide.
Shake my fell purpose, nor keep peace between
Th' effect and it! Come to my woman's breasts,
And take my milk for gall, you murd'ring ministers (1.5.47-49)
However, because Duncan is a kinsman, Macbeth has misgivings about murdering him,
First, as I am his kinsman and his subject,
Strong both against the deed; then, as his host,
Who should against his murderer shut the door,
Not bear the knife myself. Besides, this Duncan
Hath borne his faculties so meek, hath been
So clear in his great office, that his virtues
Will plead like angels trumpet-tongued against
The deep damnation of his taking-off (1.7.13-19)
Likewise, the determined Lady Macbeth is stayed by Duncan's resemblance to her father,
The attempt and not the deed
Confounds us. Hark! I laid their daggers ready;
He could not miss ‘em. Had he not resembled
My father as he slept, I had done't.
My husband! (2.2.13-17)
Further in the play, Macbeth, in his "vaulting ambition," attempts to forestall the prediction of the witches that Banquo's sons will be kings by murdering him and his son Fleance; Banquo is murdered, but Fleance flees. Later, Macbeth is tormented in his guilt by the presence of Banquo's ghost.
When Macbeth returns to the witches, he is told that he should beware of Macduff, that no man born of woman can harm him, and that he will not be defeated unless Birnam forest marches to Dunsinane. In Act V, Scene 5, Macbeth sees the forest "move" as Malcom, Siward, the general of the English forces, Macduff, and their army steal behind bushes and small trees that they have ripped from the earth. Confronted by Maduff, Macbeth confidently tells him he will not be slain by him,
I bear a charmed life, which must not yield
To one of woman born. (5.8.12-13)
But, Macduff shocks Macbeth as he retorts that he was "from his mother's womb/Untimely ripped." Then, Macduff beheads Macbeth, and the witches' prophesies are complete and the tyrant Macbeth and his "fiendlike queen" are dead.