Three witches gather as a storm rages. They arrange their next gathering: When the current battle is over, they will meet with Macbeth. They exit the stage.

Duncan, King of Scotland, enters with his sons, Malcolm and Donalbain. They are near Duncan’s military camp in Forres and, when a wounded captain passes, Duncan asks for news about the recent battle between Scotland and the invading Irish army, led by a rebel named Macdonwald. The captain says that the two sides fought like “two spent swimmers that do cling together” (1.2.8) but, thanks to the bravery of General Macbeth, the Scottish army prevailed. Macbeth has placed the rebel’s head on a spike above the castle walls. A second army appeared just as the Irish were defeated—a surprise Norwegian force launching a fresh attack when the Scots were exhausted. However, the Scottish army fought back and defeated this second army. The captain struggles with his wounds and leaves to see a doctor. The Thane of Ross arrives and tells Duncan that the Norwegians came from in Fife, assisted by the turncoat Thane of Cawdor. Duncan sentences the Thane of Cawdor to death for treason, granting his title to Macbeth.