Saigon, 1963: The city slinks toward a feverish violence. On the streets, monks set themselves alight to protest the government’s anti-Buddhist bent. Dissenters plot in secret among the Army’s ranks. In squalid prisons, students and political enemies rot in soiled tiger cages. And ensconced in Independence Palace, the insular ruling family prepares for martial law and inflates reports of their success against the Viet Cong. But the Americans backing the fragile South Vietnamese regime are growing disillusioned with President Ngo Dinh Diem and his pampered relatives and want the lot of them gone: the stubborn, inexperienced Diem, his ruthless younger brother, and particularly Diem’s sister-in-law, the woman John F. Kennedy refers to as “that goddam bitch”—the vain, calculating first lady, otherwise known as the infamous Madame Nhu.

At the peak of her powers, with her bewitching beauty and relentless ambition, Madame Nhu inflamed the imagination and provoked the hatred of the West and the Vietnamese alike. Time and Life featured her on their covers and called her a “devious” enchantress; The New York Times crowned her “the most powerful” woman in Asia and compared her to the Borgias. She was described as “proud and vain,” an “Ian Fleming character come to life,” “as innocent as a cobra,” an “Oriental Valkyrie.” Jackie Kennedy thought she had a “queer thing for power,” and the AP’s fellow in Saigon, Malcolm Browne, knew her to be “the most dangerous enemy a man could have.” Her penchant for tightly fitted sheaths and scarlet fingernails played into her image as a grande coquette, and her name became synonymous with feminine wickedness: Jackie used it as a slur for ladies she disliked, while Yoko Ono haters branded the Beatles interloper “Lennon’s Madame Nhu.”

But Madame Nhu’s rise to notoriety and influence was short-lived. In the autumn of ’63, a U.S.-backed coup deposed and disposed of her husband and brother-in-law, leaving her a hunted woman hiding out half a world away. After a few empty promises to sell her memoirs to Hollywood and make a comeback when the communists fell, Madame Nhu disappeared into obscurity—until an academic named Monique Demery tracked her down in the mid-2000s, begging her to tell her side of South Vietnam’s sad story. Thus began a cat-and-mouse game that culminated in Demery’s new book, Finding the Dragon Lady: The Mystery of Vietnam’s Madame Nhu. It’s a deeply intriguing, occasionally problematic work, one that struggles to find its way into the inner character of a narrator so unreliable, she makes Patrick Bateman look like a straight shooter—a woman still intoxicated by her faded glory and half mad from years as a recluse who comes across as ambivalently needy and terribly arrogant, conniving and pitiable, and shrewdly astute, often all at once....