More than a century ago, Dr. Magnus Hirschfeld, dubbed the "Einstein of Sex," grew famous (and infamous) for his liberating theory of sexual relativity. Today, he's been largely forgotten.

Journalist Daniel Brook retraces Hirschfeld's rollicking life and reinvigorates his legacy, recovering one of the great visionaries of the twentieth century. In an era when gay sex was a crime and gender roles rigid, Hirschfeld taught that each of us is their own unique mixture of masculinity and femininity. Through his public advocacy for gay rights and his private counseling of patients toward self-acceptance, he became the intellectual impresario of Berlin's cabaret scene and helped turn his hometown into the world's queer capital. But he also enraged the Nazis, who ransacked his Institute for Sexual Science and burned his books.

Driven from his homeland, Hirschfeld traveled to America, Asia, and the Middle East to research sexuality on a global scale. Through his harrowing lived experience of antisemitic persecution and a pivotal late-in-life interracial romance, he came to see that race, like gender, was a human invention. Hirschfeld spent his final years in exile trying to warn the world of the genocidal dangers of racism.