After dropping out of school at 13 to help support his family, he was apprenticed to a clothes dyer, a precursor to the modern dry cleaner. He spent hours figuring out how to remove stains, then read chemistry textbooks and did experiments at home. “My boss was a chemical engineer, and would answer all of my questions,” he said. On weekends he helped a chemist at a local dairy, in exchange for butter.

In the summer of 1943, he and his family were arrested and sent to Drancy, the internment camp for Jews near Paris that was the last stop before the death camps. This time, their passports saved them. Argentina’s government protested the family’s detention, so they stayed at Drancy for three months, while thousands of others were swiftly sent on to die.

Mr. Kaminsky remembered a math professor who had agreed to tutor him in the camp. “One day, when it was time for our classes, he wasn’t there. He hadn’t wanted to tell me beforehand that his name was on the list.”

The Kaminskys were eventually freed, but they weren’t safe in Paris, where Jews were under constant threat of arrest. Soon Argentines were being deported, too.

To survive they would have to go underground. Adolfo’s father arranged to get false papers from a Jewish resistance group, and sent Adolfo to pick them up. When the agent told Adolfo that they were struggling to erase a certain blue ink from the documents, he advised using lactic acid, a trick he’d learned at the dairy. It worked, and he was invited to join the resistance.

Mr. Kaminsky’s cell was one of many. His would get tips on who was about to be arrested, then warn the families, assembling new papers for them on the spot.

The group focused on the most urgent cases: children who were about to be sent to Drancy. They placed the kids in rural homes or convents, or smuggled them into Switzerland or Spain. In one scene from the book, Mr. Kaminsky stays awake for two nights straight to fill an enormous rush order. “It’s a simple calculation: In one hour I can make 30 blank documents; if I sleep for an hour, 30 people will die.”