In the beginning we meet (or hear about) our characters: King Duncan is a nice old man who was going to be taken advantage of by traitors; Macbeth is a courageous war hero who defends his king, his country, and his honor. Sweet! Time for a heroic action flick, right?
Enter Three Witches
Not so much. Along come three pesky witches/ sisters/ fates who announce that Macbeth is going to become King of Scotland. He's stoked, but quickly realizes the problem: if he's going to become king, someone else is going to have to not be king. Like the current king Duncan, and Duncan's sons, Malcolm and Donalbain.
The King is Dead; Long Live the King
With a little spurring from Lady Macbeth, Macbeth kills the king to secure the kingship. (That must have been quite a "honey-do" list.) It immediately becomes clear that the only way to hide the murder is to keep murdering, which means that the body count begins to climb.
A friendly little visit from the ghost of his murdered friend Banquo sends Macbeth into a raving fit, bringing a quick end to the banquet Macbeth has thrown together to celebrate his new kingship. We suspect that things are about to go quickly downhill.
Macbeth visits the weird sisters, who tell him some cryptic things that he interprets as: "It's cool; no one can defeat you." But, what's this? Forces—lots of forces, but King Duncan's son Malcolm—are gathering in England to fight his tyranny.
Fool Me Twice, Shame on Me
To the surprise of… no one, it turns out you can't trust witches' tales to help you out in any way. It looks like Macbeth is going to be defeated, and he goes out committed to dying soldierly death.
The last part of the prophecy fulfilled, Macbeth stands against a man not-of-woman-born. Still he fights, but good prevails over tyranny and madness. He's killed, Malcolm is named the rightful king, and everyone goes off to party at the coronation ceremony.