In the tradition of When Time Stopped and The Hare with Amber Eyes, this extraordinary family memoir investigates the dark legacy of the author’s great-grandfather, a talented German-Jewish chemist specializing in radioactive household products who wound up developing chemical weapons and gas mask filters for the Nazis.

When novelist and poet Joe Dunthorne began researching his family history, he expected to write the account of their heroic escape from Nazi Germany in 1935. Instead, what he found in his great-grandfather’s voluminous, unpublished, partially translated memoir was a much darker, more complicated story. “I confess to my descendants who will read these lines that I made a grave error. I betrayed myself, my most sacred principles,” he wrote. “I cannot shake off the great debt on my conscience.”

Siegfried Merzbacher was a German-Jewish chemist living in Oranienburg, a small town north of Berlin, where he developed various household items, including a radioactive toothpaste called Doramad. But then he was asked by the government to work on products with a strong military connection—first he made and tested gas-mask filters, and then he was invited to establish a chemical weapons laboratory. Between 1933 and 1935, he was a Jewish chemist making chemical weapons for the Nazis. While he and his nuclear family escaped safely to Turkey before the war, Siegfried never got over his complicity, particularly after learning that members of his extended family were murdered in Auschwitz.

Armed only with his great-grandfather’s rambling, 2,000-page deathbed memoir and a handful of archival clues, Dunthorne traveled to Munich, Ammendorf, Berlin, Ankara, and Oranienburg—a place where hundreds of unexploded bombs remain hidden in the irradiated soil—to reckon with the remarkable, unsettling legacy of his family’s past.