Act III opens with Banquo lamenting the witches’ prophecies and warning Macbeth that his rise may be foul. Macbeth, now king, hosts a banquet and secretly summons two murderers, later joined by a third, convincing them that Banquo and his son Fleance are enemies. He orders them to kill both that night. Lady Macbeth urges Macbeth to mask his fear and appear cheerful at the feast.

In Scene III the murderers ambush Banquo on the road. Banquo is killed, but Fleance escapes into the darkness.

Scene IV returns to the banquet. Macbeth, drinking with his guests, is haunted by the ghost of Banquo, who sits in his place. Overcome with terror, Macbeth lashes out, disrupting the feast. Lady Macbeth attempts to calm the guests, attributing his outbursts to a recurring malady, but the spectre reappears and Macbeth’s tirade intensifies, revealing his unraveling sanity.

The witches gather on the heath with Hecate, who rebukes them for acting without her and commands them to conjure new apparitions that will further confuse and doom Macbeth.

Finally, Lennox and another lord discuss the recent murders. They note that Banquo is dead, Fleance has fled, and Macduff has fled to England to seek King Edward’s support for Malcolm and Donalbain, suggesting that opposition to Macbeth is gathering.