The still-emerging stories from shrinking circles of living Jews who survived persecution by Nazis are among the most interesting and provocative. These are not the stories retold by aging relatives at family gatherings but the tightly held secrets, unforgotten deeds and buried memories that can resonate for a lifetime. Those of us who are lucky enough to hear what really happened from survivors and rescuers are often left asking what would we have done in their shoes. Would we risk our lives for a stranger?

Besa: The Promise is a new documentary film centered around that very question and two families: a Bulgarian Jewish couple and their young son, and a Muslim Albanian baker who sheltered them for a year during World War II’s darkest period. Before they flee by ship for Spain, the Bulgarians leave a three-volume leatherbound Torah with the father of the film’s main character, Rexhep Hoxha. The Jews say they'll be back for the books—a wedding present—but they never return, partly because Albania was cut off by decades of Communist rule. The books stay put as the years pass.

Hoxha’s family was among many Muslims in Albania that resisted the Nazis and helped shelter Jews. Every country in Europe had its own response to the Germans. Some happily assisted with the deportation of Jews. Others resisted—from deposed rulers to clerics and ordinary people. Albania, a poor and a mostly Muslim country, has an often-overlooked history of serious Nazi resistance.

The film opens as a grey-haired American-Jewish photographer, Norman Gershman, is discovering this forgotten legacy and sets out on a mission to interview and take pictures of elderly Albanians who hid Jews and their wartimes wards—if they still live. This quest takes him to Rexhep Hoxha, where the heart of the film begins. Gershman is as dogged as he is dazzled by documenting Albania’s forgotten history of Muslims saving Jews.

After discovering that Hoxha has the Torahs—striking evidence that his family sheltered Jews—Gershman learns that Hoxha’s father wanted to give them back to the Bulgarians. Hoxha, a simple man who owns a toy store and is as decent as he is principled, asks the documentarian if he can help find the family who rightly owns the books. The film’s title, Besa, or "promise," is a traditional Albanian creed that compels people to offer safe harbor to refugees and binds people to their promises.

The film then sets off on an unpredictable road and unwinds a series of besas. First is Hoxha’s honoring his deceased father’s goal of returning the Hebrew books. Hoxha is amazed that the Bulgarians would flee with few possessions but also the prayer books. The power of the words in the book seem to match the power of his father’s belief that one day their owner would return for them. The second besa is Gershman’s pledge to capture and tell the story of Albania’s Islamic rescuers of Jews.

These pledges are simple, fragile and noble. They get tested in the living world of ambiguities as the Gershman’s role evolves from documentary photographer into protagonist. He jumps at the opportunity, camera crew in tow, to find the prayer book’s heirs. Hoxha goes along, not seeking limelight or mugging for the camera, because he genuinely believes that returning the books to the descendants of those sheltered by his father will transform their lives. In the end, they succeed. But the results are complicated. Some people are not ready to face a long-buried past, let alone on camera.

I spent nearly two years as a journalist and author fulfilling a besa—writing a book to be published in Holland next year about how an uncle, the most famous Dutch Jewish boxer in the 1930s, kept his young son and wife alive in the first of three Nazi prisons in the war. The truth was not what was told by survivors at family dinners. It was far more interesting, compromised and difficult.

This territory—telling unknown Holocaust stories that resonate today—is tricky. People think that they have heard it all before. They haven’t. But it also is hard to fully understand what people did—and do—in wartime, and afterwards. People’s motives and actions can be as complex as their memories can be faulty. There’s always more going on than can be put on a page or projected on a screen.

Critics will probably say Besa is two films packed into one: the quest of an aging American-Jewish photographer, Gershman, which bookends the story of Hoxha’s fealty to his father’s promise to safeguard and return the Torahs. The story and relationship of the two families involved in this besa and their descendants is simply remarkable. One is left wondering how such simple human decency can endure in a world overrun by selfishness, cynicism and frequent evil. The film suggests a subtle answer: there is good in people’s hearts balancing the bad, but the good is often overshadowed and found in small unrecognized deeds.

Truth is more intriguing than fiction. But it also can be messier. Were it not for Gershman’s efforts, this story would not be told—not the particulars of various besas, not the return of the prayer books, not the larger acknowledgment that Albania’s Muslims sheltered Jews from Nazis. But at its heart, the power and appeal of this film is not the photographer’s journey. It is what his cameras and film crew found—forgotten ties and honor between ordinary people before their tribes were modern adversaries.