A twofold portrait of a pair of extraordinary characters who played a key role in the history of 20th-century ideas: André Weil (1906-1998). Entered France’s prestigious Ecole Normale Supérieure (ENS) at the exceptionally young age of 16. Taught in Europe and India through 1939. Co-founded the Nicolas Bourbaki group, which would dramatically change modern mathematics. Taught at Princeton from 1958. Simone Weil (1909-1943). His younger sister. Also a student at the ENS. Advanced degree in philosophy in 1931. As a revolutionary trade unionist, close to Boris Souvarin, left teaching to become a worker in a Renault factory. Joined the Durutti column during the Spanish Civil War, she was also a great figure of French resistance. Died of tuberculosis and despair in London. Her most important writing was published posthumously. A tough act to follow… Sylvie Weil, in what is both a panegyric and a necessary exorcism, explains with emotion and humor, The genius was bi-cephalous. My father had a double, a female double, a dead double, a ghostly double. Because in addition to being a saint, my aunt was my father’s double, they looked like twins. A terrifying double for me, because I looked so much like her. I looked like my father’s double. This disturbing physical resemblance is the starting point for a narrative weaving together memories, reminiscences from friends and relatives and personal thoughts. The result is a strong sense of these two intimidating figures that no other biographer has been able to render so intimately. Equally maladjusted to live in the real world, witnesses to and victims of History, they deserved to finally be reunited on equal footing in this book, with its perfectly balanced, accessible narrative voice.