In “That Woman,” her solid biography of the woman who was born Bessiewallis Warfield and, on Dec. 10, 1936, became the King of England’s excuse for abdicating his throne, Anne Sebba argues that her subject actually did the world a great favor. By compromising Edward VIII to the point where he could not possibly perform his royal duties, Wallis Simpson (as she became known) may have kept Britain safe from a Nazi sympathizer’s reign. Scotty Bowers, whose gee-whiz, scurrilous Hollywood memoir, written with Lionel Friedberg, is called “Full Service,” performed tireless sexual services while working as a gas station attendant and bartender. He too did favors — lots and lots of favors. Among those he claims to have befriended are “Eddy” and “Wally,” as he addressed them with all-American ease. Mr. Bowers was surprised to hear that the ex-king and his wife wanted him to embroil them in various ménages-à-trois with partners of both sexes. “This was the romance of the century, for crying out loud,” he said. Was it? Both books have the same thought about whether the love affair between the Duke of Windsor, as Edward was known post-abdication, and the Duchess, as Wallis was known after they married, was the romance of the century: no. There is abundant evidence, most recently “W.E.,” the film directed by Madonna and featuring glamorous versions of the Windsors, that this myth will persist no matter what. Mr. Bowers, happy to gossip, claims to have heard from Cecil Beaton that the Windsor myth was “a giant cover-up by the royal family and the British government to conceal the truth about Edward’s sexual preferences.” Ms. Sebba, who has actually done research, turns up considerable evidence to support this idea: “Few who knew them well described what they shared as love.” “That Woman” depicts Wallis as a woman who sought power and privilege but never expected the damage she wrought or the wrath she engendered. Born in Baltimore and married twice before she met Edward in 1931, she could be as tone-deaf as she was ambitious. Ms. Sebba points out that Wallis considered herself part of Baltimore’s aristocracy, even though her mother at one point ran a boarding house. She was delusional enough to hope, once she went to England and took up with the future king, that her own family history “would stand up against these 1066” — as in William the Conqueror — “families here.” It didn’t. And after Wallis completed her own conquest, she spent the rest of her life paying the price. She grew notoriously acquisitive. (The book pays great attention to her jewelry.) She lived in fear and frustration. And she baffled many who knew her. Ms. Sebba, like all biographers of this strangely androgynous woman, is a bit mystified by her subject’s magic powers of seduction, and wonders if Wallis’s time spent in China in the 1920s taught her any royally clever tricks. This book makes vague mention of a “Shanghai squeeze,” a “China clinch,” and “the ability to make a matchstick feel like a cigar.” “That Woman” also underscores Edward’s considerable shortcomings. There was the dreadful baby talk (as a grown man, he used words like “cwying”), the pouty selfishness, the “ethical impotence” and the total lack of intellectual curiosity and historical perspective. Ms. Sebba reports that when Edward and Wallis hired a yacht in the summer of 1936, they instructed that all books be removed from its library. Ms. Sebba presents this information in clear but not especially lively fashion. Her book is a thorough account of two not always scintillating people. The grotesque debilitation of the duchess’s final years are far more memorable here than transgressions made during her prime. And the caustic observations of contemporaries, like the Duchess of Devonshire (who suggested “Master of the Mistress” as a title for Wallis’s cuckolded second husband, Ernest Simpson), are often sharper than the Windsors’ whiny words.