Before the documentary Nuit et brouillard (“Night and Fog”) was shown at the Cannes Film Festival in 1956, French authorities censored a still image that appears in the film. In the photo, an unnamed man stands at the far left side of the frame, keeping watch over a wooden building and a scattered crowd of people. A fake beam has been drawn just over his head, concealing … something.

In the uncensored version, released many decades later, we see that what has been blocked is a jaunty rounded cap. It’s called a kepi, and any French civilian would have recognized it as part of the uniform of the French police. The officer is guarding prisoners at Pithiviers, a transit camp 50 miles outside of Paris where Jewish deportees were put on trains for concentration camps farther east. He’s not a Nazi guard or member of the SS, but there he is, aiding and abetting the Reich.

Night and Fog was one of the earliest works of its kind—a dogged, revelatory Holocaust film that showed Nazi atrocities in all their horror, down to the fingernail-scratch marks left on the ceilings of gas chambers. In exchange for covering up the kepi, preventing the French from seeing one of their own blithely supervising genocide, censors ruled that the documentary could keep its final scenes of dead bodies being pushed by bulldozers, like road rubble, into massive pits. Night and Fog’s director, Alain Resnais, considered the quid pro quo sufficient for his purposes.

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In the 1950s, would the French have been surprised by the notion that “ordinary” people had allowed or encouraged the extermination of the Jews? The war had ended only 10 years earlier; they had lived through it. They knew which neighbors had acted with cowardice or bravery, and that most, really, had lived somewhere between those two extremes. France had undergone a purge of Nazi collaborators and Vichy supplicants under its postwar leader General Charles de Gaulle, but its results, we now know, were wildly ad hoc; some perpetrators were released and others were shot in the head. De Gaulle’s insistence that good people and bad people had already been sorted, and that the French ought to forgive one another and move on, clamped down on conversations about ambiguity. Uncertainty itself was banished.

More than three-quarters of a century later, the witnesses have nearly all died, and Holocaust stories are told at a remove of three generations or more. Anyone who writes about the war must now wrestle with the idea that sometimes the facts are diluted, lost, erased, enhanced, and flat-out wrong. They also must acknowledge that a limited set of categories has come to define the people who lived in such morally compromising times: victim, villain, or hero. But what of those stories that can not be labeled as either valor or evil? Perhaps we venture only warily into this territory because degrees of culpability are so hard to parse out: Who was acting under duress, and who willingly exploited their countrymen? Who kept silent out of fear, and who was “just following orders”? This group of people might be harder to capture in retrospect, but understanding the nuance of their wartime experience is important if we ever hope to grasp how humanity holds up under the most grotesque of psychological conditions.

Burkhard Bilger didn’t know until his late 20s that his grandfather Karl Gönner had been a Nazi—a party chief, in fact, in a small village called Bartenheim in the Alsace region of France, “the great fault line of Europe,” which has at various moments in history been part of neighboring Germany. After the war, Gönner’s Nazism wasn’t discussed in the family: Bilger’s mother and her siblings were children of the war and their reticence was common for Germans at the time, who hoped to quietly bury their nation’s ugly past. For Bilger’s family in particular, with a former Nazi as their patriarch, the urge to stay mum may have been preservational. They’d been taught “never to ask questions,” he explains in his new family memoir, Fatherland. “The answers could only be dismal or self-incriminating—or worse, self-justifying.”

Bilger himself is an American. He was born and raised in Oklahoma, where his family moved in 1962, partly to escape the postwar misery of Germany and its 17 billion cubic feet of rubble. Despite frequent visits to the enchanting, almost primeval Black Forest where his parents had grown up, he didn’t attempt to parse his grandfather’s murky past until 17 years ago, when his mother, Edeltraut, received a packet of letters from a German relative. The letters, he writes, were from Gönner’s days as a Nazi occupier in Bartenheim, and they “turned his story inside out again.” So Bilger, by then a staff writer at The New Yorker, went digging.

The major animating concern of his research—years spent rooting around in town-hall basement archives, finding and interviewing elderly witnesses who knew Gönner—was figuring out what kind of Nazi his grandfather had been. A repugnant ideologue? A practical agnostic? Was it a mistake he regretted? A desperate move to keep his family alive? Without Gönner around to answer such questions, Bilger had only the records of war and contradictory accounts of hazy memories. So in Fatherland he builds a narrative that admits to its holes, that doesn’t shy away from its incompleteness while it still makes an effort, with the materials at hand, to understand life in wartime and the kind of people whose actions occupy that gray zone of morality.

Fatherland has a mission to give the widest, most generous view of the suffocating and enraging conditions in which its figures operated. In other words, Bilger is attempting a bold, nearly impossible experiment: to see if the reader can find sympathy for a Nazi—one who held chalk instead of a rifle, one who may have saved more lives than a conscientious objector. One who also happens to be his flesh and blood. He lays out the limited details he can find that might justify, or at least explain, why an ordinary man might stay committed to Hitler’s regime.

Gönner was born in 1899 in Herzogenweiler, a hilltop town so bedraggled by the lingering inequities of the feudal system and the collapse of the local glass industry that by the time he was 11, fewer than 100 citizens remained. He wanted to be a priest but instead was drafted into the German army for its last big push across the Western Front, where he lost an eye in 1918 at Liry, near the Somme. He returned home, physically and psychologically battered, too faithless to enter the priesthood and too incapacitated to return to the engineering work he’d left. Teaching was the only field that seemed viable, but he returned to a Germany of such rank economic misery that he had to beg for a working stove in the one-room lodgings he was assigned at his first teaching job at an elementary school. Gönner had been born with little and now could hope only for less. As Bilger writes, “All that was left of his faith, after the war, was a hunger for order and justice.”

Then Hitler arrived. Elementary-school teachers—the least prestigious, most impoverished sort—were intended to act as cogs in the führer’s propaganda machine, which declared that young boys were the raw material that would bring Germany back to prosperity and their teachers the force that would shape them. Gönner signed his party-membership card in May 1933, believing Hitler’s claims that “no one shall go hungry! No one shall freeze!” We know he wrote in 1932 that he had “an open commitment to National Socialism,” and that he attended two rallies at Nuremberg, though Bilger, for all his hearty research, can’t turn up much evidence of what Gönner thought as the Nazi Party evolved in the late ’30s into a runaway freight train of hate, murder, and continental ruin. But he notes that Gönner’s “principles were increasingly untethered from Nazi policies” and presents evidence that he began to perform small acts of passive rebellion.

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In March of 1942, after a year and a half working as a schoolteacher in occupied Bartenheim, he was given the official and weighty title of Ortsgruppenleiter, or “town leader,” which carried a strange kind of responsibility: The job was to liaise with Nazi officials, to file reports on suspicious villagers, to hand out fines for saying bonjour in the street. The particulars that Bilger turns up about Gönner’s interactions with locals, including French Resistance fighters, his landlady, and the town mayor, sketch an image of a man hemmed in by the existential and practical impossibility of his role.

Gönner didn’t report on villagers when they slaughtered a pig without party approval, or kept an illicit radio, or sang “La Marseillaise,” the French national anthem. The mayor’s son tells Bilger, “Your grandfather could have denounced my father a hundred times, and he never did.” Another man, one who would later hold great sway over Gönner’s fate, told Bilger’s mother that “it was because of Gönner that no family from Bartenheim had been deported. That no one had died in a camp.” A pupil lays out the ultimate contradiction: “He was a Nazi, but a reasonable one.” But he did sign every letter “Heil Hitler” and recruit boys to the Hitler Youth. He acted as the embodiment of the party in Bartenheim. He resisted and relented. The unanswerable philosophical inquiry that floats atop all of Fatherland is whether “passive resistance” in the face of a life-threatening force like Nazism ought to be categorized as a moral victory or failure.

Bilger’s approach is satisfyingly holistic. Complicating the plot is part of his intent. His broad history of Alsace situates Gönner in a region that was passed back and forth between the German and French several times in his life, a place where many of the citizens spoke only German and allegiance to any one nation wasn’t guaranteed. And the blurriness wasn’t only geographic. Alsace is an ideal setting for studying the various human impulses at work in a time of self-preservation: Some residents displayed great courage, hiding neighbors who had escaped from being forcefully conscripted into the German army, while others arose early that first morning of the occupation to greet the Nazis with cigars and chocolates. Most simply tried to get by, to avoid notice, to wait out the food rationing and random searches—in the meantime, they did what they could to survive.

The categorical imperative at work in Holocaust literature, the need to define good actors versus bad actors, is understandable—no event in recent history has cast so much of humanity into a kaleidoscope of black and white. Cultural depiction has followed the same pattern. There are the portraits of Hitler and his henchmen in films such as Der Untergang; the wide, valuable range of material depicting the genocide of the Jews, including Schindler’s List and Elie Wiesel’s Night; and the heavily documented heroics of foreign forces and resistance fighters—the volumes written about the coders at Bletchley Park, the 101st Airborne, the uprising at the Warsaw ghetto.

But what Bilger shows is how the forces moving against ordinary citizens—the threat of their own deportation, torture, or murder—could turn them into the most unimaginable of all war-battered Europeans, meek preservationists fighting individual wars for their own lives. They may have had soft spines or children to protect. Perhaps they simply didn’t know how to rise up; perhaps they were too self-concerned to care; perhaps they simply consoled themselves that the stories of evil done in their name couldn’t actually be real. As for himself, he explains, “I told myself that I would have done better. That I never would have joined the Nazi Party, never followed Hitler or left my family behind. But then everyone tells themselves that. The more I learned about life in occupied France, the more I could see soft spots in my own character, the ethical give.”

In the immediate aftermath of the war, justice came swooping down on collaborators, perpetrators, and a slew of others caught up in the mix. Gönner, for his part, ended up in a dank French prison before authorities determined his “classification”: They landed on Minderbelasteten, or “less responsible,” and then Entlasteten, “exonerated.” The French, Bilger writes, referred to the enterprise as L’épuration sauvage, the “savage purification”; nearly a third of a million people were charged with treason or collaboration. Evidence wasn’t necessarily available or explicit; there isn’t always time for legal documentation in a war zone. And over the five years of war, it was hard to discern who had resisted so passively that their behavior now looked accommodating or downright treacherous.

The fog of war also applies to citizens. In 2003, the writer and actress Anne Berest's mother, Lélia, received an unsigned postcard with only four words written on it—Ephraïm, Emma, Noémie, Jacques—the names of her grandfather, grandmother, aunt, and uncle, all of whom had died at Auschwitz. Fifteen years after the postcard dropped in their mail slot, she paired up with her mother to investigate who might have sent it, and whether it was meant as a threat or a memorial. Her novelized family memoir, The Postcard, narrates Ephraïm, Emma, Noémie, and Jacques’ life and death, Berest’s grandmother Myriam’s war spent in hiding in a neglected mountain cabin, and the detective role that Berest, like Bilger, took on to trawl town-hall archives for clues. After she relays their tragedies, Berest wants an answer similar to the one Bilger is seeking: How much culpability does that silent middle bear for the erasure of her family’s story, their possessions, their lives?

Berest’s book is a hit in France—it’s sold more than 300,000 copies and landed on the list of finalists for the Prix Goncourt. But the trouble with The Postcard is that she’s labeled it fiction and so it’s impossible to discern what facts Berest really gathered from old documents and French bureaucrats and which ones are her invention. The story is real, its outlines real, and surely, its pull on Berest is real too. But for a writer who is desperate to understand her ancestors, to learn what threads carry through from their lives to hers, concocting this jam of a story, dosed with sugar and cooked over a hot flame, is a strange and discordant decision. The same flavors emerge, but it’s chemically transformed.

I read The Postcard in tandem with Fatherland, as a sort of counterpoint. What could each book offer as a way of breaking through the haze? They share the same bones: both authors kept in the dark about their grandparents’ wartime lives, both handed cryptic documents that kick-started years-long research, both uncomfortable with the fog that hovers over their ancestry.

The Postcard—perhaps because its author writes herself as incredibly unschooled on the Holocaust, asking her mother painfully obvious questions about the war—never quite rises to the occasion. But in its most revelatory moment, Berest drives with Lélia to the cloistered country village from which her family was seized. She describes their encounters there as stilted and suspicious, as if the locals had been fearing this reckoning with their wartime behavior for decades. The current owner of their family home practically spits at them, demanding they call before they visit. Eventually they lie their way into another home, that of an elderly gentleman called Fauchère who was given their ancestors’ pigs when Ephraïm and Emma were taken into custody. Sitting in his living room is Emma’s rosewood piano. Fauchére begins to show them a photograph of their family home, one they know was lifted right off their family’s wall.

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Confusion reigns. Fauchère doesn’t quite discern their real identities, and they don’t know quite how he ended up with these items, their items, of dear sentimental value. What’s clear is that Fauchère’s glaze of plausible deniability is what allowed him to drape their piano with his own knickknacks. Berest never finds out how it came into his possession—whether through greed or ignorance—and the piano isn’t mentioned again. But a version of his name is French slang for “thief.” Berest offers him as just one link in the long chain of citizens standing at the edge of guilt.

There’s a scene from Band of Brothers that’s stayed with me for more than 20 years. The series felt dear to me because it depicted the Airborne: My own paternal grandfather jumped with the 82nd into Holland, where he was hit with shrapnel in Arnhem, just by that bridge too far. He was paralyzed and died of his wounds a few years later. All my life I’ve seen reminders of  his heroism in American war films, felt my own third-generation connection to the deadly glory of war. So when, still in high school, I watched the episode in which Dutch resistance fighters march some female collaborators in the street and shave their heads to shame them, I never questioned the women’s guilt as people who had chosen the wrong side, who had sided with evil. These women, a member of the resistance explains to American troops, had sex with Nazis for the advantage. I blithely believed in them as easily categorized monsters, as clearly as the Airborne were heroes. But as Bilger explains, his grandfather’s landlady in Bartenheim, a single mother, gave Gönner lodgings for the desperately needed rent money—and because she didn’t have much of a choice. She suffered the fate of a shaved head and a mauled reputation, despite no evidence that she’d slept with him or even given him a friendly nod. Was she a traitor or a survivor? Or something in between?