To uncover the fate of the thousands being interred at a mysterious Nazi camp called Auschwitz, a 39-year-old Polish resistance fighter named Witold Pilecki volunteered to assume a fake identity, intentionally get sent to the new camp, and then report back on what had happened to his compatriots there. Over the next two and half years, Pilecki forged an underground army within Auschwitz, thwarting the Germans from within. But as Jack Fairweather reveals, Pilecki learned the horrifying truth that the camp, compelling him to undertake a seemingly impossible escape attempt.