In a dark cave the three witches, supervised by Hecate, brew a gruesome potion and summon Macbeth. He demands knowledge of his future. The witches conjure three apparitions: a disembodied head warning him to beware Macduff; a bloody child proclaiming that no man born of woman will harm him; and a crowned child with a tree declaring that he will be safe until Birnam Wood moves to Dunsinane Hill. Macbeth, feeling invincible, also asks whether Banquo’s descendants will ever reign; the witches show a procession of eight kings, the last holding a glass that reveals an endless line of future monarchs from Banquo’s line. Angered, Macbeth commands the witches to stop and then summons Lennox, learning that Macduff has fled to England. He vows to strike at Macduff’s castle and destroy his wife and children.

In Fife, Lady Macduff and her young son discuss Macduff’s flight. A messenger warns them of danger, but murderers sent by Macbeth burst in; the son is slain and Lady Macduff cries “Murder!” as the killers leave, confirming Macbeth’s order to eradicate Macduff’s line.

In England, Malcolm and Macduff meet, lament Scotland’s ruin under Macbeth’s tyranny, and engage in a heated dialogue in which Malcolm first pretends to be more corrupt than Macbeth, then renounces those false claims and declares his willingness to lead Scotland’s salvation. They resolve to gather forces. Ross arrives with the devastating news that Macbeth’s hired men have slaughtered Lady Macduff, her son, and all who were with them. Overcome with grief and fury, Macduff vows revenge. Malcolm informs him that the English king has provided Siward and ten thousand soldiers, and together they prepare to march north to overthrow Macbeth.