A prominent civil servant, scientist, and intellectual, Taghi Erani was a pivotal figure in interwar Iran. Witness to two of the major political upheavals in the twentieth century—the rise of Pahlavi and the collapse of the Weimar Republic—he turned from fundamental science to leftwing activism and pacifism, leading to his arrest and death in prison. Younes Jalali traces his journey from Tehran to Berlin, where in the 1920s he crossed paths with the greatest German scientists and scholars of his day, including Max Planck, Albert Einstein, and Friedrich Rosen, and published seminal works on psychology and political philosophy. In the 1930s, as Reza Shah pursued rapprochement with the Third Reich, Taghi Erani was caught up in a crackdown on left-wing and pro-labor activists. His life and death offer a unique lens through which to view modern Iranian intellectual and political history.