Klara Lee of Atherton still remembers the royal blue coat and hat her mother made for her to wear on her journey to America 74 years ago. She also remembers the hard-to-procure apple her mother gave her for the trip, the one the 8-year-old refused to eat.

“That apple was like a diamond, a gem,” said Lee. “I never took one bite of that apple. I kept it and kept it as a souvenir from a parent I didn’t know if I would ever see again.”

Eventually, the piece of fruit went rotten and Lee had to throw it out and move on with the new life that was thrust upon her when, in the spring of 1939, an American Jewish couple dared to slip into Nazi-controlled Vienna to rescue her and 49 other Jewish children.

The untold story of how Gilbert and Eleanor Kraus of Philadelphia rescued 50 Jewish children, just as the doors to Jewish emigration from Europe were closing, is recounted for the first time in “50 Children: The Rescue Mission of Mr. and Mrs. Kraus,” a one-hour documentary premiering on Monday, April 8 on HBO.

Steven Pressman, the film’s San Francisco–based writer and director, learned about this incredible story unknown to Holocaust researchers and museums when his wife, Liz Perle, showed him an unpublished manuscript by her grandmother, Eleanor Kraus.

In it, Eleanor wrote how one evening in January 1939, her lawyer husband came home from work and said he wanted to rescue Jewish children from Nazi Germany. He had discussed the idea with Louis Levine, president of Brith Sholom, a Jewish fraternal organization to which he belonged. Brith Sholom had just built a summer camp in Collegeville, Pa., that had 50 extra beds for the children.

Despite her initial misgivings about the dangerous idea, as well as strong anti-Semitic social and political currents and warnings from Jewish community leaders to drop the scheme, Eleanor supported her husband and set about preparing affidavits of financial sponsorship from dozens of local friends and acquaintances.

Gilbert, in the meantime, used his friendship with a local congressman to get an introduction to Assistant Secretary of State George S. Messersmith, who in turn connected him with the U.S. consul general in Berlin, Raymond H. Geist. Gilbert came armed with research indicating that a significant number of American-issued visas actually had gone unused.

Strict immigration quotas were in effect barring the immigration of large numbers of Jewish refugees to the United States, war in Europe was on the horizon, and the American government would not provide Gilbert Kraus with any guarantees.

“This is crazy,” Eleanor wrote to her husband. “No one in his right mind would go into Germany right now.” But that is exactly what Gilbert Kraus did, and his wife soon followed, leaving the couple’s two school-age children at home.

“They went in as private citizens with no formal protection, no seal of approval from the U.S. government and no diplomatic immunity,” Pressman said.

Perle knew her grandparents well, having spent a lot of time with them after her mother died very young. However, their rescue of the 50 children was not something they told her — or anyone else — about.

Eleanor was extremely caring, elegant and a bit reserved. Gilbert was also elegant, but he had a great sense of play and curiosity about the world around him. However, according to their granddaughter, there was nothing about their personalities that would have pointed to their having taken on such a bold and risky endeavor.

“I truly think that this was a one-off. They didn’t do other daring things. They both had almost rigid senses of what was right and what was wrong, though, so in a sense, going to rescue the kids was right,” Perle said.

Upon the Kraus’ arrival in Vienna, word quickly got out within the Jewish community that an American couple had come to take children to safety. Hundreds of families tried to get their children on this American kindertransport of sorts, but only 50 were selected on the basis of physical and mental health (financial and social status were not taken into consideration) by the Krauses and Dr. Robert Schless, their German-speaking pediatrician who had agreed to travel to Nazi Germany. The oldest was 14.

“I was the 50th child chosen,” recounted Atherton resident Lee, who was the only child in an Orthodox family. “My father saw something about it in the newspaper and said he wanted to take me. My mother didn’t want me to go, because I was just getting over the measles. But my father insisted.”

Less fortunate was a little boy named Heinrich Steinberger, who had been chosen for the list but then fell ill and had to be replaced by another child. Steinberger died several years later at Sobibor.

“The most chilling thing that happened during my research for the film was my finding that little boy’s photograph among documents at the Central Archives for the History of the Jewish People at the Hebrew University in Jerusalem,” said Pressman.

The Viennese Jewish community’s archives survived the war, and they were transferred to Israel — including the questionnaires that the parents filled out for the Krauses. “Little Heinrich’s photo was the only one there, probably because the other children’s photos were used for their passports,” the filmmaker explained.

The passports were issued after a nerve-wracking meeting with the Gestapo. The Krauses were then able to take the children to Berlin, where Geist had 50 visas waiting for them, and then on to Hamburg. The group sailed for New York aboard the SS President Harding on June 3, 1939. (The Krauses held on to some of the children’s travel documents, which have since been donated to the United States Holocaust Memorial Museum.)

It was very exciting for the children to be sailing to America, but their traumatic parting from their parents at the Vienna train station was still very fresh in their minds.

“I had forgotten that my aunt and cousins came with my mother and me to the train station that night,” said Lee, whose father had left for England only a couple of weeks earlier. “A month after they interviewed me for this film I started to remember. It really hit me. I guess I [psychologically] blanked out what had happened at the train station.”

Some of the children were taken in by foster families or distant relatives. Lee, who was fostered for one year by a great-uncle and his wife, was one of the fortunate ones whose parents eventually were able to reach the United States. She and her parents moved to the Bay Area to join members of her mother’s family who had arrived as refugees several years earlier. Her father’s side of the family was killed in the Holocaust.

“50 Children” is Pressman’s first foray into filmmaking. An accomplished journalist and author, he used his research abilities to track down 15 of the surviving children (nine of whom appear in the film) and dig up everything from relevant historical State Department cable traffic to archival footage of street scenes in Philadelphia, Berlin and Vienna in the 1930s.

“The most rewarding part of all of this work since 2010 was being able in the end to show the film to the ‘children’ and their families,” Pressman said. Just as the Krauses had quickly put this episode behind them, so had the children, who built new lives for themselves in America. The full story of how it came to be that they were saved from the Nazis was something they never fully knew — until now.

“50 Children: The Rescue Mission of Mr. and Mrs. Kraus,” narrated by actors Alan Alda and Mamie Gummer, premieres at 9 p.m. Monday, April 8 on HBO.