Any nerd semifamiliar with Nietzsche knows his sister was horrid. Now a new academic biography contextualizes her horribleness historically. With analytic insight that falls short (to its credit) of actual sympathy, Carol Diethe's Nietzsche's Sister and the Will to Power (University of Illinois Press, $35) portrays Nietzsche's Nazi-friendly sibling as a shrewd, thwarted lady who made do with the hand she was dealt. Stubborn, spirited, consigned by her paltry "lady's education" to be a wife, mother, and/or groupie, Elisabeth assumed the socially acceptable role of "helpmate": first keeping house for her brother during his ten-year stint as a sickly Basel professor, then helping her crazy husband found an ill-fated all-Aryan colony in Paraguay. When both colony and husband collapsed in scandal, her brother (conveniently for her) lost his mind, and she flew back to his side, to unleash her will to power, now turbo-charged from stewing for years in resentment and cloaked in the role of selfless and devoted sister. She became her brother's keeper, his curator and PR person from hell. She created the Nietzsche-Archiv, forging documents, speciously "co-authoring" The Will to Power from notes he never intended to publish, and did his reputation the worst damage possible by allying it with his (Nazi) enemies out of sheer opportunismóbecause she didn't have a "healthy" outlet! She courted Hitler for a monthly allowance, while he in turn adopted her as a mother figure to whom he could show duty and respect. He posed with her in photo ops, while she presented the über-monster with Nietzsche's walking stick. How uncannily apt that Nietzsche's "archivist" would both preserve and tamper with his papersóembellishing and editing them to her purposes. Friedrich, of all people, understood that there is no such thing as an "objective" historian.

God's fiercest critic began and ended his life amidst Teutonic matriarchies. His father, a dour pastor, died of "softening of the brain" when young Friedrich was five (or rather, he "fell down the stairs," according to budding spinmeister Elisabeth, who would describe her husband's likely suicide as a "heart attack"). Nietzsche's alpha grandmother and two spinster aunts treated his meek, young mother like a hanger-on. Quick to sense who wore the pants, Elisabeth idealized the grandmother and dismissed her mom, whom she would later edit out biographically and financially. Infantilized mother, future Antichrist, and shrewd sis were a grotesquely enmeshed unholy trinity. A quasi-incestuous bond between the siblings, Diethe argues, would later implode in betrayal and misreadings. It's no wonder that Nietzsche would often complain of "bad air."

A founder of the British Friedrich Nietzsche Foundation, Diethe writes charmingly and takes the liberty of analyzing her characters. Like a post-Freudian Howard Cosell, she provides play-by-play diagnosis of her "monumentally insensitive" heroine who projects, displaces, denies, and even sues, to have her way. Elisabeth emerges as a brilliant flower of resentment, a well-intentioned ogress adept at the "higher swindle" of moralityóthe manipulative piety that her brother exposed as self- serving rubbish. Diethe's scholarly backstory nicely complements Ben McIntyre's journalistic Forgotten Fatherland: The Search for Elisabeth Nietzsche, chronicling his 1991 trip to "Neuva Germania" (Nietzsche's in-law's superwhite hangout), which, amazingly, remains a "Surreal Bismarckian outpost in the Paraguayan jungle" stocked with "purely" inbred descendants of the original German Lutheran settlers.

Elisabeth's brother was her great subject. She spent her life reacting to the "Dancing Philosopher" like a toxic Ginger Rogers. The pair was bound to implode upon contact with any outside erotic object. Enter Lou Andreas-Salomé, the intellectual femme fatale and free spirit, in 1882. Then retired from Basel, Nietzsche was a lonely nomad philosophizing on spiritual hygiene (between migraine and vomiting fits) while schlepping from pension to pension seeking cures for his health. Friedrich was smitten with Salomé's 'intellect' (as he wrote in his letters) and looking forward to a superbrainy ménage ŕ trois in Paris with her and his soon to be ex-friend Paul Rée (while each man secretly planned a ménage ŕ deux). Sincerely believing herself to be protecting her brother from this "adventuress," Elisabeth deployed her epistolary shit-stirring skills (writing to Lou) to scuttle the plan. Nietzsche was devastated. The siblings' relationship never recovered.

Elisabeth is that fascinating type of villain utterly convinced that she is helping even when faced with clear evidence and communication to the contrary. She meddled between the would-be Übermensch and his crush as he clearly pleaded with his sister to back off. During this Lou mishap she penned a prim, incestuous fantasy that, Diethe argues, "provides Elisabeth with the perfect opportunity of placing herself in the position of Friedrich's bride." "Coffee-Party Gossip About Nora" is a thinly veiled novella ŕ clef in which a nurturing, bookish Elisabeth-figure saves a spacy philology professor Friedrich-figure from a cunning Lou-figure, with her "impossibly thin waist, . . . high-rounded bosom, . . . and art of attracting men in spite of this somewhat ugly exterior." Elisabeth's depiction of "Lou" as a phony "highbrow" is a clear case of projection, according to Diethe, who argues that Elisabeth was most burned up that Lou (in addition to being younger, and obviously cute) was taken seriously as a thinkerónot just by Nietzsche and Rée, but by Rilke, too, and later even Freud. Still processing her Lou hatred years later, "Elisabeth cannot think up a worse insult," Diethe writes, "than to describe Lou von Salomé as a forerunner of women's emancipation."

When Elisabeth found her own mid-life love connection and ran off to Paraguay with creepy but eligible anti-Semite Bernhard Förster, Friedrich could hardly give his blessingsóalthough the couple crazily hoped he would do so, in public. "Everything has deserted me," Friedrich writes to Elisabeth, using her childhood nickname, "even the Lama has jumped away and gone among the anti-Semites (which is about the most radical method of 'finishing' with me)." With so many direct statements from Nietzsche against anti-Semites and German nationalists one marvels that he could ever have been mistaken as their fan.

The Nietzsche kids wouldn't reunite until Friedrich lost his mindóand Elisabeth seized "the God-given chance to get her hands on her brother's Nachlaß and to see herself as her brother's collaborator again. But now Elisabeth no longer had to play second fiddle to N's. In this way, she could extract revenge for N's hurtful neglect of her, while appearing to herself and others as a selfless and devoted sister."

Now the ex­first lady of an all-Aryan colony, reinstalled back home, Elisabeth proceeded to "take care" of her mother too in a vicious tug of love over Friedrich's pension, copyrights, and hence his royalties. She used biography as a tool to rule the Nietzsche roost, spending four decades attempting to "master" her brother's life story. The first volume of The Life of Friedrich Nietzsche appeared in 1895, written, Diethe speculates, "with a grudge against her mother, to whom she awards a laughably marginal role in Friedrich's upbringing." Diethe ingeniously shows how Elisabeth's reaction to being a footnote in history (as good, servile, feminine helper) actually influenced history, as her resentment fueled her "will to power" over Friedrich's destiny.

Elisabeth treated the Archiv as her salon and social-climbing vehicle, cultivating a circle of prominent Nietzsche admirers. She threw soirees where her editor entertained guests on the piano, "with Nietzsche immobilized upstairs and sometimes crying out like a wild beast." One is even more alarmed to learn: "He was occasionally put on show by Elisabeth, who allowed people to see him as a grotesque special treat. Finally her brother died on 25 August 1900." He had outlived his own wits by ten years. Elisabeth lasted until 1935.

Diethe's analytically informed study does justice to her spiritually challenged heroine while wisely not turning her into a poster child for women's oppression. Nietzsche's readers will savor the irony that his fate in the hands of his twisted sister vividly illustrates his thought. Elisabeth demonstrates the triumph of the "weak" over the "strong," while he, in turn, lived out the core perversity that generated his oeuvre: how the free spirit is mastered by the ressentiment of the slave. One rereads him with even more amazement than before and finds perfect insight into what would drive his sister to violate him so mischievously, to misread him so completelyóand with such "good" intentions.

Ever the rigorous Nietzschean, he writes to her soon after she screwed things up for him with Salomé, arguably the most painful incident for him to "amor fati" in his life: "But two things are unconditionally forbidden me by my way of thought: 1) remorse, 2) moral indignation. Be nice again, dear Lama!"

Rhonda Lieberman is a New York­based writer.