Not quite what I had in mind initially but:
Synopsis of Malcolm III Part I by Oswyn Torkhill
The Play opens at the wedding of the Earl of Moray, cousin to King Duncan of Scotland. The event is marred when the King’s Fool goes crazy declaring “that Hag hath cleaved the North but its King shall come again!” before killing himself.
King Duncan then sends his young son Malcolm off to stay with Prince Malcolm of Cumbria as part of his alliance against the King of the Isles.
In Cumbria the Prince learns that the Earl of Moray has usurped the crown, he convinces the Cumbrian to send some men with him to regain it though at the price that Cumbria shall be its own Kingdom.
At night in the soldiers camp Malcolm is lured away by the ghost of his father who warns him to beware of the witch who killed him. Confused he returns to find the camp has been butchered.
Disguising himself as a pilgrim he sets off to home vowing revenge.
On the way he rescues an old woman from witchhunters; she reveals herself as a nun heading towards a nearby shrine. When they reach the shrine her last words to him are “to the King of Kings all Kings wear Jester’s clothes”; she is gone by morning.
Malcolm comes across the camp of the Earl of Northumbria where he is warmly welcomed and entertained by mummers. Stepping out for some air he overhears a conversation between the Earl’s eldest son Osborn and an old woman; the old woman reveals herself as a witch and informs the son that the Earl’s line is foretold to become great Kings of the North when Malcolm of the Scots is buried. Osborn rushes off to find and kill Malcolm while Malcolm confronts the witch. She tells him that Osborn shall “lie among the sleepers afore ye O King of Scotland” and that his blood and the Earl’s will be needed to raise the King of the North. Malcolm flees and joins the mummers in disguise.
The mummers arrive at the Scottish Court where Malcolm discovers the usurper Moray is an imprisoned puppet of the Queen; he is captured by the new Fool who turns out to the Queen’s mad son Lulach.
The Court is then besieged by the forces of the Earl of Northumbria and the Prince of Cumbria during which the Queen reveals herself as queen of the witches and that she plans to sacrifice Malcolm, Moray, and Northumbria, and baptise Lulach in their blood as the King of the North.
Moray gives an impassioned speech to his stepson Lulach that results in Lulach freeing Moray, however they leave Malcolm imprisoned while they go to fight Northumbria.
Moray and Osborn fight to the death and Lulach flees.
Malcolm is released by the nun he rescued earlier; he arrives at battle to find the Earl of Northumbria kneeling over the body of Osborn. Their peace is interrupted by the betrayal Prince of Cumbria, Northumbria saves Malcolm’s life and is awarded with the title.
The play ends with all acclaiming Malcolm as King of Scotland.