Michael A. Ross, the author of a well-regarded study of the Supreme Court during the Civil War, thought of himself as a “meat and potatoes” legal historian.

But a decade ago in a New Orleans archive, something a bit spicier caught his eye: an 1870 newspaper article describing the “voodoo abduction” of a white toddler by two mysterious black women.

“I thought to myself, ‘This can’t possibly be true,’ ” Mr. Ross recalled recently by telephone.

The voodoo angle turned out to be hysterical rumor. But as he read on, Mr. Ross, now a professor at the University of Maryland, discovered an all-but-forgotten story of a sensational investigation and trial that gripped New Orleans and the national press for almost seven months. “There were so many other twists and turns that I was hooked,” he said.

Those twists, recounted by Mr. Ross in “The Great New Orleans Kidnapping Case: Race, Law and Justice in the Reconstruction Era,” published this week by Oxford University Press, include psychic consultations, a shadowy “House of Secret Obstetrics” and the derring-do of a crack Afro-Creole police detective versed in the latest “French” techniques — seemingly the first black detective in the United States to take part in a case that received national attention, Mr. Ross says.