Part One covers the years 1135 – 1141, from Stephen's accession to the throne of England through his capture by the forces of the erstwhile Holy Roman Empress, Matilda, the daughter and heir apparent of the recently deceased King Henry I. Having no legitimate surviving sons, Henry made his entire baronry swear to support his daughter at his death; thus Stephen's assumption of the crown was largely deemed usurpation. The action of the play encompasses political intrigue, rebellion, and civil war from the points of view of royalty, nobility, and rank and file soldiers.

Part One ends with Matilda seemingly triumphant, but her triumph and her claim to the throne unravel in Part Two as her chief general is likewise captured by Stephen's extremely able and active queen (also named Matilda), leading to stalemate.