Macbeth's plot centers around questions of power, ambition, and murder. Its main character, Macbeth, is a villainous protagonist. Upon hearing a prophecy that he will become king, Macbeth endeavors to usurp the crown. This decision, which leads to further murders and tyrannical misrule, ultimately results in Macbeth's own destruction.

The play provides powerful insight into human psychology. Its characters are not static (most certainly not in the case of Macbeth and Lady Macbeth), and we see the effects of the Macbeths' murderous ambition unfold across the play. It's worth noting that before Macbeth murders Duncan, he suffers a crisis of conscience, after which Lady Macbeth exhorts him to go through with the plan. However, once Macbeth has murdered Duncan and committed to his ambition to be king, he engineers a murder attempt on Banquo to secure his dynastic ambitions against potential rivals. Later still, Macbeth will order the murder of Lady Macduff and her children. Duncan's murder is only the opening salvo to a bloodthirsty reign; once Macbeth has committed himself, he only sinks deeper into bloodlust and single-minded ambition. Meanwhile, Lady Macbeth—his wife and coconspirator—is driven insane out of guilt for her role in Duncan's death; near the end of the play, she kills herself as a result.

This play is notable, too, for Shakespeare's use of character foils. The most prominent of these is Macduff, who occupies a similar role under Malcolm as Macbeth once did under Duncan (as the king's closest supporter). However, Macduff is loyal, unlike the murderous Macbeth, and Macduff subordinates himself to the good of Scotland, whereas Macbeth aims to dominate it. Ultimately, Macduff is described as a paragon of morality, in stark contrast to his villainous adversary. However, with this stated, these two characters are also closely tied together within the action of the play—not only through Macbeth's murder of Macduff's family, but also through the machinations of fate itself. In addition to Macduff, one can also point toward Malcolm as another effective foil to Macbeth: here we have the usurper faced by the rightful heir to the throne, and in the end, tyranny gives way to rule by virtue.