In April 1944, two men lay hidden in a gap inside a woodpile at Auschwitz for three days and nights, their mouths wrapped in flannel and gasoline-soaked Russian tobacco scattered around them to blind the dogs. This episode follows Rudolf Vrba, born Walter Rosenberg in Czechoslovakia in 1924, from his teenage refusal to be deported to his arrival at Auschwitz, where he channeled defiance into forensic observation. Working in the Canada Commando and then as a camp registrar, he counted the trucks and estimated that 1.5 million people had been murdered by January 1944.

When a new rail spur to the crematoria and drunken SS talk of Hungarian salami signaled the coming destruction of nearly a million Hungarian Jews, Vrba and Alfred Wetzler broke out and walked 81 miles to Slovakia. Their 32-page Vrba-Wetzler Report read like a cold audit of the gas chambers. We examine the agonizing delay before it reached the world, the bitter dispute over Rudolf Kastner, and the international pressure that halted the Budapest deportations on July 6, 1944, saving roughly 200,000 lives.

• Why deception on the arrival ramps was the load-bearing pillar of the camp’s operation
• Memory palace techniques versus smuggled metal tubes: how the two men say the data got out
• The Slovak Jewish Council meeting where a journalist asked why the Red Cross had not intervened
• Historians Yehuda Bauer and Randolph Braham on whether the warning could have changed anything
• Vrba’s later career in brain chemistry and his testimony at the Eichmann and Frankfurt trials