Undoubtedly, Macbeth and Lady Macbeth's relationship undergoes serious changes throughout Shakespeare's drama in which "Nothing is what is not." Before the return home of the warrior Macbeth, who has displayed brutal capabilities, Lady Macbeth becomes the dominant force once she learns the predictions of the three witches. She prays to demons to unsex her and, thereby, provide her a man's strength to perform evil. After Macbeth returns home, she takes charge, telling her husband that when King Duncan arrives he can put "This night's great business into my dispatch....Leave all the rest to me"(1.5.)
But, in Act II, Scene 1, the bloody warrior wavers in his determination as his conscience makes his "eyes...the fools o' th' other senses" (2.1.) and he becomes fearful. So, too, does Lady Macbeth display fear after her great show of bravado. For, she declares that she would have killed Duncan herself if he had not resembled her father. This remark hints that Lady Macbeth's femininity yet remains despite her demonic efforts. Still, she displays more sang-froid when Macbeth returns with the bloody daggers, and in his guilt, he asks,
Will all great Neptune's ocean wash this blood
Clean from my hand? (2.2.)
Here, then, Lady Macbeth scolds him for his "heart so white," saying that "A little water clears us of this deed" (2.2.). At this point, though, Macbeth feels regret, "Renown and grace is dead" (2.3).
By Act III both Lady Macbeth and Macbeth become confused by the equation of what is real with what is fantasy and they wear "vizards to [their] hearts" (3.2.). Yet, when Macbeth is shaken at the sight of Banquo's ghost, Lady Macbeth's resurrects her coldness, rousing her husband by asking, "Are you a man?" Macbeth replies with guilt,
Blood hath been shed ere now, i’ the olden time,
Ere humane statute purged the gentle weal;
Ay, and since too, murders have been perform'd
Too terrible for the ear.(3.4.91-94)
Further, he fears reprisals for his actions: "...blood will have blood." But, for Macbeth, his evil acts become "fair" to him because they further his ambition; however, for Lady Macbeth all dissolves and her conscience awakens, bringing upon her overwhelming guilt that she perceives as the blood of King Duncan which she is unable to wash away.
In Act V, Lady Macbeth has become completely unraveled in a "tragedy of blood." This phantasmagoria of blood is the main component of the Macbeths' ends. Lady Macbeth has a mental breakdown and loses her strong will and dies, leaving the final act to Macbeth, who grows more frightening, raging until he becomes the "nothing" that is "what is not."