Banquo knows a bit too much.
Characters: 
Banquo

Suspecting Macbeth of having played a role in Duncan’s death, Banquo leaves the castle with his son Fleance.

Macbeth

The newly crowned King of Scotland. He is afraid that Banquo knows too much about his rise to power, so he hires a gang of murderers to assassinate him.

Lady Macbeth

The newly crowned Queen of Scotland.

Lennox

A Scottish lord in Macbeth's service.

Ross

A Scottish lord in Macbeth's service.

First Murderer

A killer-for-hire in Macbeth’s employ.

Second Murderer

A killer-for-hire in Macbeth’s employ.

Attendants

Attendants to Macbeth.

Lords

Other noblemen attending King Duncan's visit to Inverness.

Servant

A servant sent to fetch the murderers.

Scene Summary: 

Banquo is starting to wonder if Macbeth is up to no good. He even suspects (quite rightly) that Macbeth is the king’s murderer. After all, he witnessed the witches’ prophecy, so he knows what Macbeth stood to gain. When Macbeth, the newly crowned king, arrives on the scene with all his attendant lords—and his wife—Banquo plays nice and then promptly leaves. Left alone, Macbeth begins to worry out loud about Banquo. Macbeth knows he’s a good guy, but he also knows that Banquo heard the prophecy. He thinks Banquo might figure things out. Plus there’s the fact that the witches foretold that Banquo’s descendants would one day be kings—not Macbeth’s. All this adds up to one thing: Macbeth wants Banquo and his son dead. With Banquo and Fleance both dead, the prophecy for Banquo couldn’t possibly come true. He has his servant bring in two men he had waiting at the gates, convinces these men that Banquo is their enemy, and hires them to do away with his one-time friend.