As act 3 begins, what is revealed about the future action of the tragedy?

Banquo is concerned that Macbeth obtained the throne through foul means. He also notes that his children are the ones who are supposed to inherit the throne, not Macbeth's. He knows that Macbeth can be treacherous and he also knows that if the witches' predictions come true, Macbeth will not have kings through his ancestry. Soon, we see Macbeth hire murderers to kill Banquo and his son Fleance.