Tourgée was an Ohioan who, as late as 1860, had teased his fiancée for her antislavery views. He was radicalized by the war and even more by his experience after it as a judge in North Carolina. Tourgée was not uncritical of Reconstruction — he called his best-selling novel based on his time in the South “A Fool’s Errand, by One of the Fools.” But he agreed with his black friends that Reconstruction’s failures followed not from Northern overreach but from timidity.

Tourgée took the case challenging Louisiana’s law on behalf of the Comité des Citoyens — black, white and Creole — led by the New Orleans newspaper editor Louis Martinet. Tourgée’s client, Homer Plessy, was a shoemaker with skin as light as Robert E. Lee’s. Tourgée argued in his brief to the Supreme Court that even if there were a clear and simple way to distinguish black from white, which there wasn’t, the law violated both the 13th and 14th Amendments, intended by Congress to make the Constitution “colorblind.”

Luxenberg’s history contains so many surprises, absurdities and ironies that it would be a shame to spoil the final chapters by revealing which justice ended up on which side. One, writing for the majority, mocked the idea that the law was a violation of the 13th Amendment and insisted that the 14th Amendment, whatever its legal objectives with respect to equality, could, “in the nature of things,” hardly have been intended “to abolish distinctions based upon color, or to enforce social, as distinguished from political, equality, or a commingling of the two races upon terms unsatisfactory to either.”

The other justice, alone in his dissent, conceded that the white race was dominant and likely to remain so. But, he argued, when it comes to the law, there is “no superior, dominant, ruling class of citizens. There is no caste here. Our Constitution is colorblind, and neither knows nor tolerates classes among citizens.” He predicted, correctly, that segregation laws would increase race hatred and that the decision would in time prove to be as pernicious as Dred Scott.

Along with the court cases and the three lovingly researched lives, Luxenberg devotes many lively and illuminating pages to race and politics in New Orleans. That’s a lot for one book. Still, the subtitle of “Separate” is misleading. Only the last section is about Plessy, and the book is not the story of “America’s journey from slavery to segregation.”

In fact, there was no such journey. There was slavery and segregation in antebellum Southern cities, just as there was segregation in the antebellum North. After emancipation, there was freedom and segregation (and exclusion and elimination).

The subtitle is also misleading because separate and unequal extended far beyond transportation and accommodations to education, employment, health care, credit, housing and criminal justice. Understanding the rash of late-19th-century segregation laws, like the rash of disfranchisement laws, means asking questions about who wanted them and why. For answers, historians have looked at the efforts (often those of liberals and progressives) to contain the explosive mixture of race, gender and political conflict in growing Southern cities; the emergence of the black middle class and the entry of black women into politics; the Woman Suffrage Movement; the Populist Movement; the determination of black people to hold on to the rights and power they gained during Reconstruction; and the determination of white people to take those rights and that power away.

Segregation is not one story but many. Luxenberg has written his with energy, elegance and a heart aching for a world without it.