Of all the calumnies leveled at the Jews down the centuries, none has been as lethal as the blood libel. This infamia, which “branded the Jews as bloodthirsty ‘others’ who deserved to be killed,” as the late, revered historian Robert Wistrich explained it, has appeared in a dizzying range of locations. From the 12th-century kingdoms of England and France, the blood libel, which accused entire Jewish communities of murdering Christian children for ritual purposes, spread to other territories and cultures, among them Poland and Lithuania in the 17th century, Damascus in the 19th century, and Kiev as recently as 1913. “The Murder of William of Norwich,” by the Princeton academic E.M. Rose, is a landmark of historical research into the grotesque 800-year history of blood-libel accusations. The book traces in forensic detail—Ms. Rose calls it microhistory—the circumstances around the emergence of the first recorded blood libel in history and in so doing demonstrates how the libel was used as a tool in wider Christian struggles over power, money and territory, in which the Jews became all too convenient pawns. The story of an apprentice boy named William, who would eventually be canonized as St. William of Norwich, begins in eastern England in 1144, less than a century after the Norman Conquest. As Ms. Rose demonstrates in her mesmerizing study, it was a dark time for England. Violent civil war raged between King Stephen, the grandson of William the Conqueror, and his cousin Matilda, who challenged him to the throne. The situation was considered so dire that, in the words of one chronicler of the time, it was as if “Christ and his saints were asleep.”

William was an uncommonly bright lad, able to communicate fluently with both Anglo-Saxons and Normans as well as with the burgeoning Jewish community of Norwich, then England’s second city after London. As an up-and-coming leathermaker, William would have been noticed by the Jews of Norwich, some of whom were involved in that industry. Shortly after being offered a post as assistant to the cook who served the local archdeacon—a position of advanced status—William was found dead in a nearby woodland, his body horribly mutilated.

In the immediate aftermath of his death, William’s fate excited little interest. Adolescent suicide, Ms. Rose points out, was common at the time. The bruises and cuts on his body could have been the result of abuse by peasants, who regarded the act of suicide as satanically inspired.

But in 1150, the story of William’s death adopted the features of a religious cult, thanks to the wholesale revision of William’s story by the Benedictine monk Brother Thomas. Herein lies Ms. Rose’s key contribution: While the blood libel as a phenomenon across the ages retains certain shared features, she says, historians ignore at their peril the “significantly different cultural and social forces at work in those periods.” In the case of young William, it was the failure of the Second Crusade of 1147 that gave a “master narrative” to the snippets of unreliable detail about his death. While theology, particularly the growing appeal in the 12th century of the cult of the “innocents”—children whose stories of suffering replicated that of Jesus himself—conveniently segued into libel, the coarse material interests of the crusaders themselves, chiefly their willingness to use violent means to cancel their debts, were arguably of greater importance.

Enter Simon de Novers, a knight from the environs of Norwich who was among those who “straggled home” to England in 1149 stricken by military failure and crushing personal debt. Joining the Crusades was an expensive business, and churches and abbeys were often reluctant to lend money to aspiring crucesignati as they set out on their expeditions to the Holy Land. Like other knights, Simon was compelled to turn to Jewish moneylenders for financing. Unable to pay his main creditor, a Jew known by the name Deulesalt (“May God Save”), the knight, in contemporary parlance, had him whacked.

Deulesalt’s murder resulted in a lengthy trial for Simon de Novers, motivated by the king’s desire to prove that no crime in his domain would go unpunished. Fortunately for Simon, his lawyer was the bishop William Turbe, a crafty character who devised an ingenious defense. Deulesalt, Turbe insisted, had led the Jews of Norwich in executing William in the manner of Jesus, even placing a crown of thorns on his head. In killing Deulesalt, Simon had thus avenged the noxious crime of odium fidei—the killing of a Christian by Jews driven by hatred of the dominant faith.

King Stephen’s personal verdict resulted in a stalemate: Simon’s trial was indefinitely suspended, and the Jews of Norwich, who countered Turbe’s falsehoods at the king’s court with patiently Talmudic reasoning, also escaped unscathed. Yet Turbe’s fatuous arguments became sacralized in Brother Thomas’s manuscript, “The Life and Passion of William of Norwich,” which underwent several revisions over the next two decades in a bid to provide Norwich a patron saint, like other great cities. (A new edition of Thomas’s deadly myth has just been published by Penguin Classics.) Among the many charges made by Thomas was that the killing of gentiles was a necessary condition of Jews regaining their ancient homeland—a portrait of bloodthirstiness reinvented for our own time by opponents of Zionism who endorse the dismantling of Jewish sovereignty with the same zeal that the monks and bishops of old urged the expulsion of their Jewish neighbors.

Ms. Rose’s fascinating treatment of the narrative around William and its gradual dispersal throughout England and France is followed by examinations of four similar blood libels in the ensuing decades. One of those, in the French town of Blois in 1170, when the body of a child was dragged out of a river, is deemed by Ms. Rose as a “watershed” moment in the development of the libel. Eager to assert his independence from the king, a local count named Thibaut blamed the drowning on local Jews who until then were able to rely on royal protection. Thirty members of the Blois community were burned to death.

No longer was Judaism, as the author puts it, “a licit but subordinate religion”—a doctrine primarily associated with St. Augustine, for whom the persistence of Judaism was a reminder of the greater truth of Christianity. They had been transformed into the deadly adversaries of Christendom, deserving only death and expulsion. Within a century, the Jews would be expelled from France and England.