Act III of Macbeth opens with Banquo. He paces a corridor, wondering out loud about the prophecies. He notes that all of the prophecies for Macbeth have come true; however, he wonders if Macbeth "played foully" or cheated his way into the kingship. Banquo also wonders if the prophecy about his own sons being kings might become true, putting this at the forefront of this act as a focal point.

Banquo doesn't ponder long, however, because soon enough Macbeth himself enters onto scene. Macbeth invites Banquo to a feast that he is holding that evening. Banquo accepts, telling Macbeth that he and his son are going for a leisurely horse ride that afternoon. Macbeth also mentions that they should address the issue of Malcolm and Donalbain because he believes they may be plotting against him.

Soon, Macbeth is left alone in the hallway. A servant approaches to tell him that some men have come to see him. Macbeth sends the servant away to fetch the men and, alone on stage once again, he launches into a soliloquy. He ponders the issue of Banquo, noting that he is the only person in Scotland whom he fears because of his strength, wisdom, and good character. Macbeth also wonders if he has killed Duncan only to have Banquo's sons become kings instead of his own descendants; the thought infuriates and frustrates him.

The men Macbeth summoned appear on the scene, and it is revealed that they are actually murderers whom Macbeth has hired to kill Banquo. Macbeth reminds the murderers of the plan, insisting they make sure to kill Fleance as well. He also reminds the murderers of their reason for killing Banquo- that on some past occasion, they were wronged by him. To justify his actions, Macbeth also says to them that he would kill Banquo himself, if he could do it without upsetting their mutual friends.

In scene two, Lady Macbeth worries about being disconnected from her husband. He appears to be making major decisions with her, having not told her of his plans to murder Banquo until this point. This scene marks another turning point for these two characters. Whereas in the first two acts, Lady Macbeth is making many of the decisions, Macbeth has now taken charge. In addition, whereas his conscience seemed to rule over his decisions and he felt remorse over his actions in the first two scenes, this has begun to dissipate. He now has no hesitations about arranging for Banquo's murder. He is now driven solely by his ambition, and he is willing to do whatever is necessary to keep the power he has gained.

In scene three, the two murderers are joined by a third murderer. They attack Banquo, killing him. Fleance, however, manages to escape. This detail is important because it allows for the possibility that Banquo's heirs could still replace Macbeth's descendants on the throne.

In the next scene, Macbeth and his wife are hosting a great feast. On their way in, Macbeth meets with one of the murderers, who informs him that Banquo has been killed but Fleance has escaped. This makes Macbeth fearful for his future because he knows that the prophecy could still be fulfilled. Though shaken, he goes in to the feast only to see the ghost of Banquo sitting in his chair. However, no one else at the banquet can see this ghost. Lady Macbeth scolds her husband, and Macbeth takes his seat, seeing that the ghost has disappeared.

However, Macbeth sees the ghost again, prompting an outburst that alarms his guests. Lady Macbeth makes excuses for him, telling their company that Macbeth has had an ailment since childhood that causes visions. She prompts the guests to leave, which they do, leaving Macbeth and Lady Macbeth alone.

Banquo's ghost is an important symbol here, likely a manifestation of Macbeth's guilt over his atrocious crimes. However, it is important to note that this is not Macbeth's first hallucination. In act II, he also witnessed the hallucination of a dagger, likely as a result of the conflict he experienced over killing Duncan. These hallucinations suggest that Macbeth's action are taking a great toll on his mental state. In Shakespeare plays, characters often have a fatal flaw, some characteristic that leads to their downfall. Macbeth's flaw is his ambition, and the reader can see in this scene how his ambition begins to unravel his sanity.

After the ghost's disappearance, Lady Macbeth remarks to her husband about some rumors she has heard about Macduff. According to a servant-spy, Macduff does not plan to return to court, an action that could be interpreted as openly treasonous. It is also revealed here that Macbeth keeps a paid spy in each of his subject's home, showing his paranoia. Macbeth decides that he will try to find the witches again in order to glean more information about his own future.

In scene five, the witches have gathered once again. They meet with Hecate, the goddess of witchcraft. Hecate expresses her displeasure at being excluded in the plans to meddle with Macbeth's future. However, she decides to take over the plans, and tells the witches that when Macbeth comes to visit they will show him visions that fill him with a false sense of security.

In the final scene of the act, Lennox-one of the thanes-walks with another lord. The two discuss recent goings-on in Scotland, particularly Banquo's murderer. Conveniently, this murder was pinned on Fleance because he fled the scene. However, both of these men are not so easily fooled, and they suspect Macbeth in the murder. The lord tells Lennox that Macduff has fled to England to get help from Malcolm and the king of England to overthrow Macbeth. Having caught wind of these plots, Macbeth is preparing for war. Both Lennox and the lord, however, hope that Macduff and Malcolm will be successful.

In this act, it becomes clear on many levels that, though Macbeth has power, he is danger of losing it all. Not only has Fleance survived the assassination attempt, but Macbeth's thanes are clearly suspicious of him and unhappy with his tyrannical rule.