It is after midnight in Inverness. Banquo talks with his son Fleance and notices the stars aren't shining. He prays for angels to "restrain in me the cursed thoughts that nature gives way to in repose" (2.1.7-8).
Banquo is also struggling against ambition. Earlier Macbeth begged the stars to hide (1.4.51). They have.
Macbeth enters. Banquo tells Macbeth his sleep has been troubled by dreams of the weird sisters. Macbeth claims never to think about them. But he suggests they talk about the witches soon, and adds that if Banquo supports him when the time comes he'll reward and honor Banquo for it.
Banquo is open about the troubling "dreams" the witches have inspired in him. Macbeth, who has decided to act on his own selfish ambition, is not.
Banquo says he'll be receptive to what Macbeth has to say provided he loses no honor in seeking to gain more. Banquo and Fleance head off to bed.
Banquo believes true manhood means acting honorably—just what Macbeth used to believe.
Alone, Macbeth sees a bloody dagger floating in the air. He can't grasp it, and can't decide whether it's a phantom or his imagination. "Nature seems dead" to him (2.1.50).
As Macbeth gets closer to the murder, nature starts to go haywire.
Offstage, Lady Macbeth rings the bell to signal that Duncan's attendants are asleep. Macbeth goes to murder Duncan.
Interesting that in Macbeth, most of the violence happens offstage.