On a sweltering July night in 1925, Henry Gerber—a German-born post-office worker living in Chicago—heard a pounding at his door. Several uniformed police officers shoved their way inside, confiscated his diaries and personal files, and arrested him. Only at the police station, when Gerber saw two of his gay and bisexual friends sitting for mugshots, did he start to realize what was going on: He was being persecuted for launching what was likely America’s first gay-rights organization.

In an article he wrote for a gay magazine in 1962, Gerber likened the next few days to an “Unholy Inquisition.” After police discovered the existence of his group—the innocuously named Society for Human Rights—Gerber spent five days in jail before being released on bail. Although he was never charged, he was fired from the post office. Many of his gay acquaintances refused to be seen with him, fearing undue attention.

If we visualize the history of the gay-rights movement in the U.S. as a scatterplot, Gerber’s Society for Human Rights is an outlier dot, a lone outburst of activism that arrived nearly three decades ahead of its time. Traditional accounts of U.S. queer history tend to begin in the 1950s, when organizations such as the Mattachine Society and the Daughters of Bilitis ushered in the first, tentative era of activism. Then, the story goes, the 1969 Stonewall riots unleashed the movement’s more radical, liberationist phase. The Society for Human Rights, which existed for less than a year, from 1924 to 1925, and which aimed to create a political constituency around gay rights, is often reduced to a footnote. But the existence of Gerber’s organization complicates things: If queer people were organizing themselves in the 1920s, what happened to the movement in the 30 years or so in between?

In An Angel in Sodom: Henry Gerber and the Birth of the Gay Rights Movement, Jim Elledge, a veteran chronicler of gay Chicago, makes the case that we should consider Gerber not an asterisk, but a forefather of the gay-rights movement—one who would influence later generations of activists. In telling Gerber’s story, An Angel in Sodom offers a rare glimpse into a 1920s and ’30s queer world about which we still know precious little. After Gerber, the movement didn’t disappear—it just went underground.

Born in Passau, Germany, in 1892, Henry Gerber first arrived in Chicago at the age of 21 with his younger sister. There, he found a hidden but vibrant gay scene that spanned saloons, vaudeville shows, and street corners in the city’s Towertown neighborhood. A chagrined city investigator once estimated that “twenty thousand active homosexuals” lived in Chicago. Anyone could enter their world, if they only knew where to look.

The police were active too. Gerber was arrested for having sex with men, and around the time the U.S. entered World War I, he was committed to an insane asylum. In 1919, Gerber, who had up until then gone mostly by his birth name, Josef Dittmar, unofficially changed his name in order to hide his medical history. He enlisted in the Army and was dispatched to Koblenz, Germany, to work as a proofreader for a military newspaper. There, Gerber found one of the world’s most open and progressive gay scenes. He was particularly inspired by the Institute of Sexual Science, a research organization headed by the renowned sexologist Magnus Hirschfeld, who gave trans people formal ID cards that helped them avoid arrest for cross-dressing.

Gerber returned to Chicago in 1923, buoyed by a newfound understanding of what gay activism could look like. “Unlike Germany, where the homosexual was partially organized,” Gerber wrote in 1962, “the United States was in a condition of chaos and misunderstanding concerning its sex laws.”