In Macbeth’s castle, Banquo and his son Fleance walk through the halls. Though Fleance is tired, Banquo cannot sleep. Lately, his nightmares have kept him awake. They come across Macbeth and Banquo notes his surprise to find that Macbeth is still awake. The king, Banquo explains, is asleep. Banquo and Macbeth discuss the witches and the prophecy, though Macbeth claims not to have thought about the matter at all. They agree to talk later, and Banquo and his son exit. In the hallway, Macbeth sees a vision of a dagger that floats in the air. He cannot determine whether it is real or a “fatal vision” (2.1.36); the handle points at Macbeth and the tip points at the room where Duncan is asleep. Macbeth decries the hallucinatory dagger as a metaphor for his unease over what he must do. He finds a renewed resolve. A bell tolls elsewhere in the castle. It is a signal from Lady Macbeth, a sign that Duncan’s chamberlains are asleep. Macbeth heads for Duncan’s chambers.

Lady Macbeth appears in the hallway that he husband has just left. She imagines Macbeth murdering the king and—hearing Macbeth make a noise—worries that the chamberlains have awoken.