Two books: One a memoir by Ingeborg Day, a former editor of MS Magazine, and another an erotica by Elizabeth McNeill.

The themes of the books may be separated like heaven and earth are, but as Sarah Weinman unravels, they are penned by the same person.

In her memoir, The Ghost Waltz, Day among other things, grapples agonizingly with her Austrian father's Nazi past. 

As Elizabeth McNeill, Day writes about a grueling, sadomasochistic relationship with a man, which ends after 9 1/2 weeks.

During the time Day wrote the erotica under a pseudonym, she was an editor of the feminist MS magazine. Weinman writes that there is no knowing whether the magazine found out about this "other" Day, but the character in the erotica does have a day job as a New York City editor. She confides that she has no problem keeping her sanity and her day-persona intact, while at night she walks in the shoes of the sex-charged woman:

Throughout the entire period, the daytime rules of my life continued as before: I was independent, I supported myself (to the extent of my lunches, at any rate, and of keeping up an empty apartment, gas and phone bills at a minimum), came to my own decisions, made my choices. The nighttime rules decreed that I was helpless, dependent, totally taken care of. No decisions were expected of me, I had no responsibilities. I had no choice.

I loved it. I loved it, I loved it, I loved it, I loved it.

Ultimately when Ingebor Day is let go of as a MS editor, the reason isn't, Weinman argues, her secret sexual identity, but her anti-semitism. 

Weinman strikes up a fascinating connection between the two books as they are threaded inside the same personality thus:

Reading “Ghost Waltz” and “Nine and a Half Weeks” side by side, Day’s vulnerabilities come shimmering into view. Both books examine the consequences of relationships marked by withholding—be it her lover’s effortless domineering humiliation or her parents’ shutting the door on discussing Herr Seiler’s deep-seated Nazi ties. The absence and emotional deprivation that young Ingeborg detects and learns to live with permeated her adult life, and must have been tied up with her brief but toxic relationship, in which submissive infatuation was mistaken for something more. The pair of books allow us access to Day’s mind, demonstrating her obsessive need for order in the face of extreme emotional chaos. But they also offer insight into a particular moment in history ripe for both a self-excusing memoir of a Nazi past and a self-punishing memoir of sexual obsession. The prolonged social upheaval of the decade threw secrets into the light and enabled the discussion of formerly taboo topics. To pilfer from the title of one of the more popular self-help books of the period, if Day’s book-length confessions enabled her to be O.K., then perhaps we could be similarly O.K. with our own darkest fears and desires.