Within months word got around that Mr. Wisnia was a gifted singer. He started singing regularly to Nazi guards and was assigned a new job at a building the SS called the Sauna. He disinfected the clothing of new arrivals with the same Zyklon B pellets used to murder prisoners in the gas chamber.

Ms. Spitzer, who’d noticed Mr. Wisnia at the Sauna, began making special visits. Once they’d established contact, she paid off inmates with food to keep watch for 30 minutes to an hour each time they met.

Their relationship lasted several months. One afternoon in 1944 they realized it would probably be their final climb up to their nook. The Nazis were transporting the last of the camp prisoners on death marches and destroying evidence of their crimes.

As crematories were demolished, there were whispers within the camp that the Soviets were advancing. The war might end soon. Mr. Wisnia and Ms. Spitzer had survived Auschwitz for more than two years while most prisoners never made it past a few months. In Auschwitz alone, 1.1 million people were murdered.

During their last rendezvous they made a plan. They would meet in Warsaw when the war was over, at a community center. It was a promise.

Mr. Wisnia left before Ms. Spitzer on one of the last transports out of Auschwitz. He was transferred to the Dachau concentration camp in December 1944. Soon after, during a death march from Dachau, he happened upon a hand shovel. He struck an SS guard and ran. The next day, while hiding in a barn, he heard what he thought were Soviet troops approaching. He ran to the tanks and hoped for the best. It turned out to be Americans.

He couldn’t believe his good fortune. Since he was 10 years old, Mr. Wisnia had dreamed of singing opera in New York. Before the war, he’d written a letter to President Franklin D. Roosevelt requesting a visa so he could study music in America. His mother’s two sisters had emigrated to the Bronx in the 1930s, and he’d memorized their address. Throughout his ordeal in Auschwitz, that address had become a sort of prayer for him, a guidepost.