Act three of Macbeth is were Banquo's death takes place.
The scene opens with Macbeth speaking to Banquo, Macbeth asks him to come to dinner but Banquo declines. Macbeth asks 'Ride you this afternoon?' to which Banquo replies 'Ay my good Lord.'
However, shortly after this scene Macbeth is seen conversing with to Murderers he has hired to kill Banquo. He says he can't kill Banquo himself because 'certain friends that are both his, and mine, whose loves I may not drop.' I think that this is just an excuse because Macbeth knows he can't personally kill Banquo because he is his friend.
Things do not go as planned because, although the murderers were told to kill both Banquo and his son Fleance, Fleance manages to escape hearing his fathers bloodied cries behind him 'O treachery! Fly good Fleance fly, fly, fly! Thou mayst revenge. O slave!'
I think this will have strong significance later in the plot, it could possibly lead up to Macbeth's death.
I think that Banquo's words 'fly' have a very strong yet subtle meaning. For instance it could relate back to the old mans words in act two about an owl slaying the hawk. At the time, those words were meant to represent Macbeth, the owl, slaying the King, the mighty hawk. However this time I believe the meaning has slightly differed. Fleance is now the owl and Macbeth has become the Hawk.
The lead witch, Hecat, makes an appearance amongst the other witches. She moans at them for meddling with out consulting her first but other than that accepts what has happened and decides to let things fall in place.
Later there is a dinner scene with Macbeth and guests. Macbeth sees the ghost of Banquo although no one else can see it. I believe this is because the guilt of knowing Banquo is dead because of him becomes to much. It is also the first time Macbeth shows his unwell state of mind in front of someone other than Lady Macbeth.