Scene I of Act I of Macbeth begins with three witches or, as they are referred to in the play on some occasions, the three weird sisters. The sisters gather round and make plans to confront Macbeth while a storm rages in the background. Weather in Shakespeare plays is often notable, and this is certainly the case here. The witches, supernatural and powerful, are dangerous just as the raging storm is.

One of the witches also utters a key phrase in this scene stating, "fair is foul and foul is fair." Basically, this idea means that good is bad and bad is good or, in other words, that nothing is exactly as it seems or as it should be. This is an idea that will be echoed time and time again in the play.

Scene II then pans over to a recent battle between King Duncan of Scotland and a group of invaders, led by a rebel named MacDonwald. The king has also been pitted against an army from Norway, allied with the Thane of Cawdor. A captain reports having seen Macbeth and Banquo fight bravely against the rebels and, in particular, Macbeth killed the traitorous MacDonwald. As a reward, King Duncan determines to give Macbeth the title of Thane of Cawdor and sends Ross as his messenger to deliver to news to Macbeth.

The following scene then shifts again, this time to a location near the battlefield, where the witches have gathered once more. The discussion between the witches here is quite revealing about their characters. One remarks that she has been off killing swine, while another tells how she is plotting revenge on a woman's husband because the woman refused to give the witch some of the chestnuts she was snacking on. Clearly, these witches are not pleasant beings. Macbeth and Banquo stumble across these witches, commenting that they "look not like th' inhabitants o' th' earth," meaning they look supernatural in their appearance.

The witches greet Macbeth by calling him Thane of Glamis-the title that he already holds. However, the witches then hail him as Thane of Cawdor. Macbeth is, of course, puzzled by this, not knowing why they would greet him by another man's title. This is a key example of dramatic irony. Dramatic irony is when the audience knows something that a character does not. Here, the audience knows that Duncan is already planning to make Macbeth Thane of Cawdor, but Macbeth has no idea.

Finally, the witches hail Macbeth as future king. Laughing, Banquo demands his own fortune of them, and the witches tell Banquo he will be both greater and lesser than Macbeth because his sons shall be kings. Macbeth demands an explanation from the witches, but they disappear into thin air.

Banquo and Macbeth discuss this strange occurrence but they are interrupted by the arrival of Ross and Angus. Ross, having just come from the king, tells Macbeth that Duncan bestows upon him the title of Thane of Cawdor. Macbeth is shocked because it seems to him that the witch's prophecy has come true in part. This sets him wondering how the final part of the prophecy-Macbeth as king-might also come true. He wonders if the crown will fall to him through the nature course of circumstance or if he would have to take action to make it so.

The following scene in this act takes place at Duncan's castle. Cawdor has been executed for his betrayal of his king, and Duncan's son, Malcolm, reports that Cawdor went bravely to his death and confessed to all of his crimes. At this time, Duncan publically declares Malcolm to be his heir. Though Macbeth outwardly celebrates with all of Duncan's followers, he inwardly knows that Malcolm is an obstacle to be overcome if he wants to be king. Duncan announces his plans to celebrate at Macbeth's castle, and Macbeth departs before everyone else in order to make the necessary preparations.

Some of Duncan's character is also revealed here as he remarks upon his own inability to judge people accurately; he confesses that he had trusted the MacDonwald completely. This is some clear foreshadowing, or a hint of what is to come, because it shows how Duncan is overly trusting. If Macbeth plots against him, he will likely never see it coming.

Scene V shifts now to Inverness, Macbeth's castle. Macbeth's wife, Lady Macbeth, has received a letter from her husband, detailing his encounter with the witches. Immediately, she knows that she must do whatever it takes to convince her husband to seize the crown by whatever means necessary. In a lengthy soliloquy, or speech she makes alone on stage, Lady Macbeth discusses how she must put aside her femininity so that she can be filled "from the crown to the toe top-full / Of direst cruelty" so that she can murder the king. Meanwhile, she fears Macbeth is too "full o' th' milk of human kindess" to kill Duncan. Macbeth enters a short time later, and he and his wife discuss the possibility of getting rid of Duncan.

In Scene VI, Duncan arrives at Macbeth's castle. In an ironic comment, Duncan remarks upon the peacefulness of Inverness not knowing, of course, that while things might seem peaceful, the Macbeth's are plotting his murder. This ties back in the witches' initial comment about "fair is foul;" clearly, this is an example of something seeming good that is actually bad.

In the final scene, Macbeth is alone on stage. In his soliloquy, he wrestles with the idea of killing Duncan. On the one hand, Macbeth does want the crown and he is willing to do what is necessary to take it. However, on the other hand, Macbeth's conscience nags at him for several reasons. First, Macbeth knows that Duncan is a good king and he has done nothing to deserve an untimely death. Secondly, Macbeth knows that he should be protecting Duncan as his follower and as his host.

Lady Macbeth enters and berates her husband when he tells her he no longer wants to go through with the murder. She tells him her plan: they will get Duncan's guards drunk and, while they are sleeping, sneak in to kill the king. They will then smear the blood on the guards to implicate them. Inspired, Macbeth reluctantly agrees.

A key component in this first act is the development of the characters of Macbeth and Lady Macbeth. Macbeth, though ambitious, does have a conscience because he knows the precise reasons why he should not kill Duncan. Lady Macbeth, on the other hand, shows no hesitation or remorse at the thought of killing Duncan; she is eager to seize power. This interplay between the characters also calls into question the ideas of masculinity and femininity. In Shakespeare's day, the traditional role of women was that of a caring, compassionate nurturer. Lady Macbeth's willingness to cast aside her femininity for cruelty is a reversal of the expected order of things. Additionally, Lady Macbeth even calls Macbeth a coward, questioning his manhood for his inability to take what he wants. The development of these characters, as well as the concepts of masculinity and femininity, will be further developed throughout the play.