Banquo thinks about how if the weird sisters prophecy about Macbeth becoming king is true then it must be possible that Banquo's line will be next for the throne.
"Yet it was said it should not stand in thy posterity, But that myself should be the root and father of many kings." (Banquo act 3 scene 1)
Macbeth enters accompanied by Lady Macbeth, Ross, Lennox, Lords, and Attendants. Macbeth is having a feast tonight and is wondering if Banquo would like to attend. Banquo accepts but says he will go for a horseback ride this afternoon.
"Tonight we hold a solemn supper, sir, and ill request your presence." (Macbeth act 3 scene 1)
In order to solidify Macbeth's position on the throne he feels that Banquo and his son Fleance must be taken care of.
"We have scorched the snake not killed it. She'll close and be herself whilst our poor malice remains in danger of her former tooth." (Macbeth act 3 Scene 2)
Macbeth asks Lady Macbeth to be as nice as possible to Banquo at the party tonight so that when the murder is finished the last memory of them together was in a positive light.
"Let your remembrance apply to Banquo; Present him eminence both with eye and tongue." (Macbeth act 3 Scene 2)
The three murderers attack and kill Banquo when he arrives from his horse ride with Fleance.
"Let it come down!" (Murderer act 3 Scene 3)
In the attack Fleance manages to slip away unharmed while Banquo didnt fair to well.
"O treachery! Fly, good Fleance, fly, fly, fly!" (Banquo Act 3 Scene 3)