The underestimation of women was a resource that Ida (at left) and Louise Cook deployed for enormous good. Photograph from Daily Mail / Shutterstock

Ida and Louise Cook were not the sort of women who attracted the attentions of strangers. In the late nineteen-thirties, the sisters, unmarried and in their thirties, were living at home with their parents, in a middle-class London suburb. Louise worked at a secretarial job for the civil service. Ida, the younger by two years, had quietly discovered a knack for writing romance novels, and, under the pseudonym Mary Burchell, had begun publishing them with Mills & Boon, the British equivalent of Harlequin. The sisters’ friends respected them as ardent and remarkably knowledgeable fans of opera, with a circle of close acquaintances that included several of the world’s leading divas. But to know any of that you’d have to see beyond their unprepossessing appearances. The Cook sisters were plain and gawky and ingenuous. They often dressed in clothes that Ida had sewn at home from patterns she found in women’s magazines.

The underestimation of women, especially women who might be dismissed on the basis of their looks, was a resource that Ida and Louise deployed for enormous good. Once Ida had earned some real money from her writing, they began making frequent trips back and forth to Germany, flying out of Croydon Airport on Friday nights, in an era when commercial air travel was not at all common, and returning by train and boat from the Netherlands, in time for Louise to get to her office on Monday morning. They did not elicit quite the curiosity that you might expect. That held true, at least some of the time, even when they returned to England draped in fur coats and jewelry that they had not been wearing when they left.

The jewels and furs they sneaked out were not for themselves but for refugees from Nazism, mostly Jewish but some political, whom they were working to get to safety—finding people in England who would vouch for them and take them in, assembling their papers, and eventually purchasing a flat in London where people in transit could comfortably stay. To help support themselves in their new lives, refugees could sell the glamorous belongings that the Cook sisters managed to spirit away. For their work on behalf of persecuted European Jews, Ida and Louise would eventually be honored as Righteous Among the Nations by Yad Vashem, the World Holocaust Remembrance Center.

Ida Cook’s memoir of their efforts, which was published in 1950 as “We Followed our Stars,” was reissued, in 2008, as “Safe Passage,” and is still in print. I picked it up in a used bookstore this summer, when the mistreatment of families at the border was again in the news. In it, Ida explains how the smuggling part of the sisters’ homespun mission worked. “It was fairly simple at first, but then came the time when the Hitler guard used to come on the train at the frontier and check everything you had, and when you came out you were checked again.” They adapted by entering at one checkpoint, wearing no jewelry, not even wristwatches, and leaving through another, positively glittering. That way, they wouldn’t see the same officials twice, “and there was no one to notice that we had become rather overdressed English girls with a taste for slightly too much jewellery.”

Once, the Cooks were planning the escape of a milliner from Berlin, called in the book only by her first name. Alice, a non-Jew married to a Jewish man, was “soft-voiced” and endearing, with lovely white hair and “hyacinth-blue eyes,” but she had “her own brand of moral courage, too.” Her husband had fled to the Netherlands, and would later be rounded up and killed; Alice had refused to make hats for the wife of the Nazi foreign minister, Joachim von Ribbentrop, and now urgently needed to leave Germany. The Cooks had helped her obtain a guarantee for legal refugee status in England, but she would not be allowed to bring her only financial resource, her jewelry. The sisters took it, but they had “a very bad half hour” at the border, when S.S. men got on the train and lingered in the corridor outside the Cooks’ compartment. Somehow, the sisters avoided having to open their handbags, where they had stuffed all of the jewelry they couldn’t plausibly wear. But they had been prepared for such an inspection: they were going to do their “nervous British spinster act and insist, quite simply, that we always took our valuables with us, because we didn’t trust anyone with whom we could leave them at home.” The Cooks had found that telling a lie that made them look meek and foolish was sometimes their best bet. So, too, was a hidden-in-plain-sight approach. Once, Ida recalls, she stuck a particularly large diamond brooch onto the front of her cheap sweater and forced herself to wear her coat open: surely that way no one would take the outsized pin for anything but costume jewelry from Woolworth’s.

Partly, it was that kind of wry, modest gallantry that made me fall in love with the Cook sisters. There was something so charming and almost dotty in the way Ida describes things getting “a bit awkward” when you knew they must have been terrifying, or in the wonderment she expresses after learning that one of their “cases” had been a valuable asset of the underground resistance—that “all those years ago, we’d been heroines, without the pain of knowing it!” Ida and Louise remind me of the redoubtable female leads in early Hitchcock movies, like “The Lady Vanishes” or “The Thirty-nine Steps,” so I was delighted to learn that there is, in fact, a movie in the works. Donald Rosenfeld, a former president of Merchant Ivory Productions, told me that he is co-producing, with Andreas Roald, a feature film about the sisters, which is slated to begin production in the fall of 2020. A biography of the Cook sisters, by Isabel Vincent, an investigative journalist, is due to be published in Britain next year. I imagine there is plenty more to tell, especially about the prewar lives and postwar fates of the refugees the sisters helped, than Ida Cook does in a book that is often discreet.

In the meantime, “Safe Passage” is well worth reading at a moment when so many of us feel numbed and overwhelmed by the gravity of the world’s problems. The book wasn’t written as a guide for activists or aid workers, but it is, incidentally, full of such advice. Working mostly outside of established organizations, the Cook sisters made up their own rules of conduct, but they seem to have been sound ones. They tried, for example, to keep families together. “Part of a richly happy family life ourselves, we knew that it would be poor comfort to be rescued oneself if a beloved mother or father, brother or sister still lingered in danger and the shadow of death,” Ida writes. “Whenever possible we worked right through a family, hoping one day to reunite them somewhere in the world.”

The sisters’ own family—a younger brother and particularly their parents—did them the service of “representing normal existence,” and thereby keeping us “fairly steady.” One day, when Ida came home from Germany, she went straight into the kitchen, where her mother was making “pastry, which is after all, one of the basic things of life.” Ida was crying, anguished by the thought of all the people she would not able to save. If her mother “had stopped and made a sentimental fuss,” Ida felt she would have broken down entirely. Instead, her mother went on making pastry and, in a few minutes, when Ida was a little calmer, said, “It’s no use tearing yourself to pieces. You’re doing the best you can. Now tell me all about it.”