When Ohio newspapers published the story of Alice Chenoweth's affair with a married man, she changed her name to Helen Hamilton Gardener, moved to New York, and devoted her life to championing women's rights and decrying the sexual double standard. She became one of the most sought-after speakers on the 19th-century lecture circuit, published seven books and countless essays, supported herself, hobnobbed with the most interesting thinkers of her era, visited 22 countries, and was celebrated for her audacious ideas and keen wit. Opposed to piety, temperance, and conventional thinking, Gardener eventually settled in Washington, DC, where her tireless work proved, according to her colleague Maud Wood Park, "the most potent factor" in the passage of the Nineteenth Amendment.

Free Thinker is the first biography of Helen Hamilton Gardener, who died as the highest-ranking woman in federal government and a national symbol of female citizenship. Hamlin takes active steps to unpack the racism that underpinned the women's suffrage movement, giving listeners a detailed view of Gardener's politics and the contradictions inherent in them. Her life sheds new light on why it was not until the passage of the 1965 Voting Rights Act that the Nineteenth Amendment became a reality for all women.