The body was discovered on a March afternoon in 1911 by two boys exploring one of Kiev’s many caves in search of treasure. It was that of a boy just about their age, dressed in only a shirt and underwear, his hands tied behind his back, slumped over next to his school books. Little Andrei Yushchinsky had met a terrible end, stabbed as many as 50 times by an awl.

In a violent city like Kiev, there was no reason to expect that the murder would give birth to one of the most notorious legal cases in the early 20th century, an international cause célèbre that would attract world-wide attention, exposing the cynicism and moral bankruptcy of czarist Russia. Today, in the wake of the Holocaust and other genocidal bloodlettings, the Beilis Case, as the scandal came to be known, is all but forgotten. But Edmund Levin’s “A Child of Christian Blood: Murder and Conspiracy in Tsarist Russia” reminds us that, in its day, the murder rivaled France’s Dreyfus Affair as the ugliest expression of modern anti-Semitism. His is the most thorough, reliable and readable book on the subject to date.

When the initial investigation by local authorities—marked by almost criminal incompetence that saw the horrendous mishandling of the crime scene—produced no clear suspects, police felt pressured to make an arrest. Through a mixture of political agitation and scheming on the part of the authorities, Russian nationalists and those most likely guilty of the crime, Mendel Beilis, a Jewish clerk at a brick factory near the murder scene, was charged with the murder. That the evidence against Beilis was nonexistent was irrelevant to the prosecution, for the accused was on trial not as an individual but as a representative of his tribe—a Jew guilty of ritual murder.

The naked anti-Semitism of the Beilis Case isn’t shocking in the context of late-czarist Russia, infamous for bloody pogroms and a massive web of laws restricting nearly every facet of Jewish life. But as Mr. Levin, a writer and producer at ABC’s “Good Morning America,” stresses in this deeply researched and carefully argued book, the deadly fantasy of the Jewish “Blood Libel” neither originated in Russia nor resonated there with the same force as in other parts of Europe.

The lie of the Blood Libel was created by a Welsh monk, Thomas of Monmouth, in the 12th century, following the murder of a young boy. According to Monmouth, Christian blood was required in a secret Passover ritual, without which the Jews would never be able to return to their ancestral land. From England the myth spread to Europe, where, in various guises, it took on a remarkably tenacious life. The final decade of the 19th century saw as many as 79 major ritual-murder cases across the Continent. But, as the author points out, the majority of these were in Austria-Hungary and Germany. Indeed, the Blood Libel was most prevalent in Catholic Europe, not Orthodox Russia, where it was perceived, even if only subconsciously, as something alien to the native culture.

Russia, however, turned out to be the only place in Europe where a case of Jewish ritual murder would be wholly embraced by the central government. Historians have proposed different explanations for this bizarre fact. Some have claimed it was meant as a way to derail a bill in the Duma, Russia’s parliament, that would have abolished the Jewish Pale of Settlement, which generally restricted Jews to the Russian Empire’s westernmost provinces, where they had traditionally lived; other scholars have seen in it a calculating attempt to rally xenophobic Russians behind the czar and the traditional order, or even a concession to pressure from the far right.

Mr. Levin points out the errors of these interpretations, following instead the path elaborated by the late Hans Rogger, the pre-eminent scholar of Russian anti-Semitism. This wasn’t an example of populism, Rogger insisted: The czarist government distrusted, indeed feared, its people, and it repeatedly resisted popular involvement in what it perceived as its affairs. Rather, the explanation for the government’s behavior is to be found in Russia’s autocratic system, particularly in its last autocrat.

Nicholas II was preternaturally anti-Semitic. He believed in the cabal of World Jewry and the “Yid-Masonic conspiracy” aimed at Christian Russia. He also believed in the reality of Jewish ritual murder. “In pursuing this mad venture, then,” Mr. Levin writes, “the tsar’s personal ideology, not politics, was the necessary condition, the indispensable factor.” Ambitious and cynical high government officials desperate to please their czar were crucial in creating the Beilis affair.

The case provoked universal outrage. Open letters denouncing the fantastical nature of the charge were written in France and Germany, signed by the likes of Anatole France and Thomas Mann. Sir Arthur Conan Doyle, G.B. Shaw and H.G. Wells were among the luminaries who attached their names to a letter published in the Times of London. Once the trial got under way, protesters took to the streets in cities across Europe and America. Even small towns like Kenosha, Wis., could boast that their citizens had come out to protest an injustice being committed on the other side of the globe. (Yet America, as Mr. Levin notes, wasn’t immune to anti-Semitic violence: Leo Frank, a Jew, was falsely convicted of murdering a Christian girl and dragged from his cell and lynched in Georgia in 1915.)

The Beilis trial lasted over a month, yet it took the jury only an hour and 20 minutes to come to a decision: not guilty. No one was ever convicted of the crime, and to this day no one, not even such an authority as Mr. Levin, can definitively say who committed it. As for Mendel Beilis, the life he had known was destroyed. With his family he moved to Palestine in 1914 and then to the U.S., settling in the Bronx. He had trouble finding work, eventually being reduced to selling copies of his memoirs door-to-door. In Kiev today, some still place flowers on Andrei Yushchinsky’s grave, a martyr, in their deluded eyes, to the perfidious Jew.

Mr. Smith is the author of “Former People: The Final Days of the Russian Aristocracy.”