Mark Mazower, a noted British-born historian of the darker sides of 20th-century Europe, has now turned to the history of his own family, bringing his formidable research skills to subjects that often prove as elusive and ambiguous. The “you” in his book’s title is Mazower’s father, Bill, an enigmatic and recessive figure who, but for his fluent Russian and colorful relatives, might pass for an ordinary Oxford-educated middle-class Englishman. But it is Mazower’s grandfather Max, with his adventurous, cosmopolitan past and unresolved mysteries, who steals the show.

Part of this is because of the latter’s radical past. Living in Vilna in the early years of the 20th century, Max (born Mordkhel Mazower) was a member of the Bund, a Jewish socialist organization based in the Pale of Settlement in the old Russian Empire whose success in its time was remarkable. By 1905, the Bund’s registered membership was 35,000—almost three and a half times as large as its socialist competitor, the Russian Social-Democratic Labor Party. But its memory has been eclipsed by the achievements of its rivals: The Bolsheviks, a wing of the RSDLP, seized the historical limelight with the October Revolution of 1917, and the Zionists, the Bund’s competition on its Jewish side, similarly cemented their place in history with the creation of the state of Israel.

But another reason for Max’s fascinating appeal is the set of more personal mysteries buried just beneath the surface of his life. Max’s past as a Russian-speaking Jewish revolutionary, almost never discussed with his family, accorded oddly with his bourgeois English present. There was also the child that Max brought back with him from Europe before World War I, who may or may not have been his son, and whose mother’s identity was long unknown to the rest of the family.

Mazower tells a story that is both a family saga and something larger. Through Max, he reacquaints us with a forgotten strain of radicalism that once dominated life in the Pale. Through the stories of the Toumarkines, the family of Max’s wife, Frouma, Mazower gives us a glimpse of the other realities that Max and his descendants might have experienced had they either remained in the Soviet Union or become part of the Russian emigration throughout Europe. Mazower’s painstaking detective work solves some of the mysteries around Max’s life; others remain unsolved but will resonate in the reader’s memory.

Mordkhel Mazower was born in Grodno around 1874. After his father’s death, when Mordkhel was about 14, he moved with his mother and younger siblings to Vilna (now Vilnius), a city outside the Pale but with a large Jewish population. Max, as he styled himself from this period on, seems to have had little formal education, yet he somehow quickly acquired good Russian (the family’s language in Grodno was Yiddish) and the manners and bearing of a Russian intellectual. Smartly dressed in a tie and high-buttoned waistcoat, with a neatly trimmed mustache and goatee, Max was almost a dandy—an appearance well suited to a young man with prospects who had secured a responsible job with a solid Jewish shipping company.

But this up-and-coming young man, like many of his Jewish contemporaries, was also a socialist. Not only did Max join the Bund, but he was active in its illegal revolutionary organization. His underground career included two terms of administrative exile to Siberia and involvement as a Bundist organizer in the Lodz uprising in 1905. After escaping from Siberia for a second time, Max, like many others in the dispiriting years after the failure of the 1905 Revolution, moved out of the realm of clandestine revolutionary politics and back into the business and professional world aboveground.

For Max, this meant a London-based job working for the Yost Typewriter Company, which was keen to expand into the Russian market and valued his Russian-language skills. This was the beginning of Max’s residence in England, which lasted until his death in 1952, but it was not the end of his trips to revolutionary Europe and Russia. Shortly before the First World War, the Yost company sent Max as a typewriter salesman to the Russian capital of Petrograd (formerly and subsequently St. Petersburg), where he witnessed the Bolshevik takeover in October 1917. He returned to Russia a few years later, this time on a trip to Petrograd and Moscow as the representative of a steel manufacturer in Sheffield.

It was on one of these sojourns that Max met Frouma Toumarkine, the well-educated daughter of a Russian Jewish merchant family with socialist sympathies, who was then a young widow with an 8-year-old daughter. They married in 1924, when Max was 50, and he brought his (non-English-speaking) bride and her daughter to London, installing the family first in rented accommodations around Hampstead Heath and later in a home of their own on Oakeshott Avenue, one of a row of mock-Tudor houses with generous private gardens hidden in the back.

Max and Frouma’s marriage was evidently a happy one, and it brought him a more settled, if less exciting, life. In 1925, the couple had their only child, William Joseph, Bill for short. (His middle name was that of his grandfather, and his first was taken from Shakespeare, one of the few English names that his mother knew at this point.) Frouma soon learned English but never lost her heavy Russian accent, while Max apparently spoke English like a native (albeit an educated and middle-class one) and dressed to the end of his life neatly and formally in three-piece suits, his jackets buttoned high.

Despite the bourgeois appearance of the Mazower family, 20 Oakeshott Avenue became (thanks to Frouma) a warm and welcoming place for Bundists and, increasingly throughout the 1930s, for Jewish refugees from the continent. The Mazowers’ circle included Vera Broido, a Russian writer and Menshevik married to the historian Norman Cohn, and Emma Goldman, whose work for the anarchists in the Spanish Civil War brought her periodically to London. But much of the rest of their milieu was Jewish Highgate and Golders Green; their friends had leftist sympathies but were rarely political activists. Instead, as Mazower reports, they included “businessmen, more or less successful, import-export traders in timber or coal…a tailor and a pioneering Yiddish art critic.”

Eventually, the Great Depression would hit Max hard and he would suffer from increasing ill health, though he remained a businessman to the end. Max died in 1952, six years before the birth of his first grandson, Mark.

A distant, elderly father, Max was uncommunicative about his past, and his son Bill was perhaps too incurious to ask. So it was left to Mark to chase down material for the family history from archival sources, as well as from the memories of more distant relatives. His narrative, as befits current biographical fashion, includes much detail on his unsuccessful efforts as well as his successes. The reader becomes used to leads that end up going nowhere and to documents, unearthed with difficulty, that infuriatingly fail to resolve the author’s problems—“a useful reminder,” Mazower notes, “that archival sources raise as many questions as they answer.”

With his father, Mazower had more immediate access. But there were still plenty of things left unsaid. Bill grew up fluent in Russian and French (on Frouma’s side, there were family connections to the Russian émigrés in France) but was otherwise “indistinguishable from any English boy of his age,” with a liking for cricket, gardening, and tinkering. There were also, however, Bill’s two half-siblings—Frouma’s daughter Ira and André, whose relation to the family was somewhat unclear—who were decidedly more exotic, and Mazower has done extensive research on these two. Ira, who was nine years older than Bill, was apparently quite close to her half-sibling when he was growing up, but as an adult she came to espouse values—elegance, fashion, dramatic self-presentation, social status, and money—that were alien to many in the family, so much so that Mazower remembers that, in her periodic visits to Oakeshott Avenue, Ira was “disdained” by Bill and his family. André, the other older half-sibling, had a troubled relationship with Max and not much of a relationship at all with Bill, who was 16 years younger. Away at school and university for most of the time that Bill was growing up, André hovered “like a sort of specter in the background.” In later life, he changed his name, settled in Spain, converted to Catholicism, and became a right-wing anti-Semite.

The great mystery of André, which preoccupies the author as much as it did André himself, concerned who his parents were. Since Max had brought him to England as a baby just before the First World War, the presumption was that Max was his father, though André himself later questioned this. But finding out who André’s mother was proved to be one of Mazower’s historical-research tours de force. Her name was Sofia Krylenko, and—satisfyingly, from a biographer’s point of view—she turns out to have been the sister of Nikolai Krylenko (a Bolshevik leader who won fame—or infamy—as a public prosecutor in political cases), Elena Krylenko (who married Max Eastman), and Olga Krylenko (the secretary of Lev Kamenev, a member of Lenin’s Politburo and a sometime political opponent of Stalin). In one of those “small world” coincidences that occur in histories of the international left, Sofia was also at one time a close friend of Asja Lacis, the Latvian femme fatale with whom, in the 1920s, Walter Benjamin fell in love, and she was herself a deeply committed revolutionary prone to extremism and with an aversion to domestic life.

The circumstances of Sofia’s relationship with Max, and how Max ended up with her baby, remain murky, and Mazower never quite tracks down any answers in this regard. Always considered somewhat crazy by her family, Sofia spent her later years in the Soviet Union, where she was eventually committed to a mental hospital, probably for a combination of medical and political reasons, not long before her Bolshevik brother Nikolai was executed as an enemy of the people.

Frouma’s extensive family—five siblings in Russia, as well as two in Paris—is equally thoroughly researched, and through it we get an even fuller portrait of the Russian left’s history. One of Frouma’s siblings married an ex-Menshevik economist who, but for his refusal to testify, would have been a star witness in the so-called “Menshevik trial” in 1931, prosecuted by none other than Nikolai Krylenko. Still, when family communication between Britain and the Soviet Union—interrupted in the late 1930s—was resumed at the end of the 1950s, it turned out that “the Terror had struck the family, but the Toumarkines had risen in Soviet society nonetheless.” Among the success stories were an eminent pediatrician and Frouma’s remarkable younger sister, Natalia, who became a doctor in the NKVD service, working in the postwar years in a Krasnogorsk camp where her patients included Field Marshal Friedrich Paulus and other German POWs, who remembered her as “the angel of Krasnogorsk.”

According to Mazower family lore, Natalia had met her third (and last) husband, an engineer named Magnitov, when they were both working on the NKVD’s Volga-Don Canal construction project, she as a doctor and he as a prisoner. This information startled me. In my capacity as a Soviet historian, I had also encountered Magnitov: He was one of the rehabilitated “bourgeois wreckers” whose story was featured in a famous work of Soviet propaganda of the early 1930s, Belomor, co-edited by Maxim Gorky. According to the Belomor account, the construction site in question was the White Sea–Baltic Canal, not the one connecting the Volga and the Don farther east, and Magnitov makes his cameo appearance as a former bourgeois so completely rehabilitated by labor that he has become a new man: “Engineer Magnitov thinks of the old engineer Magnitov, and for him that person is already alien. Magnitov calls that person ‘him.’” That this beneficiary of Soviet reeducation ended up marrying into the NKVD adds another dimension to the concept of rehabilitation.

Altogether, the Mazower-Toumarkine family networks are fascinating, all the more so because of their members’ habit of tangentially encountering celebrities. Bill was not like this. Even when, as at Oxford, he involuntarily brushed shoulders with the famous, or those soon to be so, he took care not to cultivate them. (“In general, those men Dad was drawn to tended not to be intellectuals nor to achieve fame afterwards,” Mazower notes.)

This likable trait can nevertheless be frustrating for the biographer son. Bill clearly did not want a life of celebrity, drama, and adventure. When asked in his university-admissions interview which century he would have liked to have been born into (in England, it went without saying), he answered the late 18th century, because of its calm and civility. Still, Oxford was a “liberation” for him, as Bill told his son in a rare personal statement, partly because it was the first time in his life that he had come across girls. Overall, his years at Oxford were gregarious and happy ones, despite the fact that he and other young men were living under the shadow of the Second World War, then ongoing, and imminent call-up into the armed forces.

Bill served in the Home Guard in the last year of the war and was then sent for officer training at Sandhurst before his appointment to the Royal Corps of Signals in 1946 (he had added some engineering training to his Oxford studies of history and Russian). Service in occupied Germany with the British Army of the Rhine followed, an experience that he found depressing. Demobilized in 1948, Bill returned to Oxford for a year and then went out into the world as a trainee manager with Lever Brothers, where he worked for 30 years, mainly in a London office supervising the construction of breweries in West Africa.

At wartime Oxford, Bill made friends with a number of middle-class non-Jewish Englishwomen, internationally minded, energetic, and nonfrivolous (unlike his half-sister Ira)—women who “valued the arts and self-improvement, and took the politics of the public good seriously.” But he seems to have had no thought of marrying any of them, telling his mother “in all seriousness” (she obviously found his earnestness rather funny) that “he would not marry until the end of the war, having no desire to leave a widow.”

After demobilization, however, Bill’s time had come. The Mazowers moved largely in Jewish circles, even if his parents shared what the author calls “the whole Bundist suspicion of more or less any form of organized religion.” (When Mazower asked his father what Jewishness meant for him and his parents, “given their Christmas trees and Easter feasts, an unease with Jewish festivals and total horror of synagogues,” Bill replied that it was “chiefly that sense of solidarity that he and his parents had felt with the refugees trying to escape Germany and Austria after the Nazis came to power.”) And so, when it came time to choose a wife, Bill selected a young Jewish woman—the daughter of a small textile manufacturer in Manchester and the granddaughter of the Yiddish writer Sholem Asch—whom he had met through friends of his mother: “old-fashioned matchmaking in the Eastern European style.” The pair got married and went to live in Golders Green, only a few miles from 20 Oakeshott Avenue, in a very similar house with a big garden at the back.

Telling the story of his father, Mazower faces several quandaries: How do you write of a life characterized not by high drama and violent upheaval, but by “resilience and tenacity and the virtues of silence and pragmatism and taking pleasure in small things”? And how do you penetrate the defenses of someone who, when pushed to talk about himself, tended to “shift from the personal to the sociological with the speed of light”?

Mazower recognizes these problems at the outset but never fully overcomes them. With a “surface diffidence and modesty and courtesy that masked, in the right circumstances, a real underlying warmth and slight melancholy and the desire to help and be useful,” Bill remains largely a closed book to us, for all his son’s efforts.

At least in part, this may be because of Mazower’s implicit policy not to introduce the living members of his family as important figures in the story. As a result, we never see Bill’s interactions with anyone in his immediate family except his wife (from her letters to her own mother and siblings) and the author, on a one-to-one basis rather than as part of a broader family dynamic. The father-son relationship that the author describes has the very English quality of reticence, marked by a respect for the other’s privacy and a lack of easy physical intimacy and overt expressions of love.

These same qualities no doubt explain Mazower’s unwillingness to probe further in his interviews with his father, but he has at least, in writing this book, found a way to express his great affection for the man. This comes across especially in the last chapter, “The Shed,” though here, too, Mazower treads lightly: The portrait is less of his father than of his father’s workplace in the back garden of their home, and it is not so much the words that are moving as the author’s unexpectedly beautiful photographs of tools neatly arranged, carefully labeled containers on shelves, and honeysuckle growing around the shed door.

These were the small things that his father took pleasure in, the place where he made himself useful to the family by repairing what was broken, just as he had done as a helpful child in his mother’s house down the road. To be sure, it was a far cry from the grand passions and conspiracies of revolution that had once animated his own father, Max, or even the upheavals and privations experienced by his mother’s siblings in the Soviet Union and as émigrés in France. But that distance was Bill’s choice, a way of handling a family history that he didn’t disown but also internally resisted.

Mazower, one suspects, had his own internal conflicts about writing on such personal topics. His book places his family history firmly within the dark history of 20th-century Europe of which he has written so compellingly. Yet he ends What You Did Not Tell not with a gloss on history but with a tribute to the reticent English father who did his best to turn away from the dark.