Macbeth opens with our Three Witches, who speak in what seems like riddles, telling that they will meet Macbeth, stating also that "fair is foul and foul is fair," a theme present throughout the work.
In Scene II, Duncan, King of Scotland, is met with a sargent who recounts the events of a battle. Macbeth and Banquo are introduced as the captains. The sargent tells of Macbeth's heroic, and arguably brutal, actions on the battlefield when he killed Macdonwald - "...he unseam'd him from the nave to the chaps, / And fix'd his head upon our battlements." Duncan learns his Thane of Cawdor has committed treason and renames Macbeth as such. Ross is sent to inform Macbeth of this.
The Witches, however, reach Macbeth before Ross does. They tell him he is to become Thane of Cawdor and also king, which baffles Macbeth. Banquo is told he will not become king, instead, his sons will. Ross then arrives and tells the pair of Macbeth's new title. The Witches' truth begins to make Macbeth hungry to become king. He writes to his wife, Lady Macbeth, to tell her of the news and of the prophecy. When a messenger tells her Duncan is coming to stay for the night, she, more cunning than he, devises a plan to murder him. The regicide would be carried out by Macbeth in order to seize the throne.
At first, Macbeth is hesitant of this, countering that Duncan is his king and his kinsman and has been nothing but lovely to him and the rest of the kingdom. Lady Macbeth assures Macbeth that this must be done in order to take power. She threatens his manhood, saying he is less than a man if he does not do this, and argues that if Macbeth did not kill Duncan, she would. Lady Macbeth tells her husband that all he has to do is kill Duncan and the rest will be taken care of.
That night, Macbeth murders the king. Lady Macbeth had drugged the guards and afterwards painted them with blood to simulate their guilt. The next morning, Duncan is found, stabbed to death. His sons Malcolm and Donalbain decide to flee, fearing they will be next [to be murdered]. Macbeth first experiences guilt directly after the murder, telling his wife, "Will all great Neptune's ocean wash this blood clean from my hand? No, this my hand will rather the multitudinous seas incarnadine, making the green one red" (Act II, Scene II) [ref].
Macbeth is now king, yet he is suffering from paranoia caused by the guilt of his murder. He also becomes more greedy for power, and decides he must kill Banquo and his son, Fleance, so the throne will not be taken from him. Macbeth hires murderers to kill them both, but Fleance escapes. That night, the Macbeths host their friends at the castle, Banquo, of course, is not there, but Macbeth sees his ghost (denoted Ghost of Banquo). Macbeth is speaking to his own throne where he perceives Banquo to be seated; everyone else in the room thinking Macbeth is ill.
The Witches meet Macbeth once again, telling him to beware of Macduff.
Lady Macbeth and her husband's roles have almost been switched; she is now feeling guilty whereas he is even more power-hungry. Lady Macbeth is thought to be sick, sleepwalking when she delivers one of her most iconic lines; "Out, damned spot! out, I say..." [ref]. Soon after she is pronounced dead.
The play ends with Macduff beheading Macbeth, ending his short-lived reign of 'terror.' Malcolm returns and becomes the new King of Scotland. Before exiting, he closes the play with, "...his dead butcher and his fiend-like queen, / Who, as 'tis thought, by self and violent hands / Took off her life; this, and what needful else / That calls upon us, by the grace of Grace."