Attention, “Game of Thrones” fans: The most enjoyably sensational aspects of medieval politics — double-crosses, ambushes, bizarre personal obsessions, lunacy and naked self-interest — are in abundant evidence in Nancy Goldstone’s “The Maid and the Queen: The Secret History of Joan of Arc.” Goldstone’s premise, innovative but not outlandishly so, is that Joan’s rise from poor, illiterate farmer’s daughter to mystical champion of French nationalism during the Hundred Years’ War was largely orchestrated by Yolande of Aragon. Yolande, who was the Duchess of Anjou and Countess of Maine as well as the Queen of Aragon (among other titles), was also the mother-in-law of the dauphin, Charles, whose military triumph over the occupying English and coronation in Reims were the two great causes espoused by the saintly, if warlike, Joan. As Goldstone sees it, Yolande’s political genius goes under-recognized.

“The Maid and the Queen” describes two ways exceptional women found to exercise power in the Middle Ages. Yolande — who ran Aragon while her husband (and, later, her son) pursued a fairly hopeless claim to the throne of Sicily — raised money, sponsored advisors, negotiated strategic marriages and otherwise worked, often indirectly, to further the interests of her six children. She backed the Armagnac side in the protracted French civil wars that weakened the country to the point that Henry V and Henry VI of England found it ripe for the picking. The other side, the eel-like Burgundians, formed on-again, off-again alliances with the limey invaders.

Charles, who became dauphin (heir to the French throne) only after his four elder brothers died, had gone to live with Yolande in her castle at Angers at age 11, when he was betrothed to her daughter, Marie. His father was intermittently mad (a situation that led to much of the chaos in France) and his own mother was so self-serving that eventually she repudiated him as the illegitimate product of an adulterous affair in order to appease a more useful ally. (Goldstone finds persuasive proof of his legitimacy.) Charles called Yolande his “Bonne Mère” (good mother) and, as Goldstone writes, “became very attached to her, relying on her judgment and reflexively turning to her in moments of distress. No one had more influence with Charles than Yolande.”...