They met in the full flush of the WashPo’s post-Watergate glory: Lescaze the seasoned, sophisticated White House correspondent, Ms. Darling the flirtatious, verbose and unbearably self-conscious girl reporter—a “tatterdemalion creature,” as she puts it, modeling herself after wayward women throughout history and literature. “I aim for a carefully calibrated equipoise between overweening arrogance and abject self-hatred,” she told Shelby Coffey III, then the assistant managing editor of the paper’s famous Style section, sort of a Teen Beat idol to the young female journalist set (he had, Ms. Darling writes breathlessly, “a charm he wielded with the deftness of a stiletto”). Lescaze, meanwhile, “gleamed like a brand-new car.” Before long, Lynn and Lee, who had a wife and three children, were gazing longingly at one another over martinis, bantering about Schubert and Samuel Beckett, and in a scene that is mercifully left to the imagination, falling into bed.

Their story might’ve ended in a tangle of sheets … except they also fell in love. Lescaze left his family and Ms. Darling, “a brilliant wild child of the sixties” (so says the jacket copy), a radicalized Army brat and sexually free ’Cliffie, was somewhat surprised to find herself mired in a shabby ménage. The tatterdemalion creature’s career was in tatters, her reputation in ruins. Worse, she was no longer the ingénue of the fairy tale, but (the horror) a stepmother.

What happens next is awful, the stuff of Russian literature—except as Ms. Darling is continually reminding us with faint astonishment, it’s her life! The wild child seems unable to settle comfortably into any adult role. “I didn’t know how to be married now that I was a mother,” she writes after bearing Mr. Lescaze’s third daughter, “just as I didn’t know how to be a writer, or a woman for that matter.” In an act that aptly summarizes her book, and perhaps her generation, she grabs a mirror and with dismay examines her birth-ravaged private parts.

Necessary Sins is not a memoir in the complete sense, more an extended elegy for a love affair in the tradition of Lillian Ross’ Here But Not Here. Ms. Darling’s parents and friends are merely supporting players in her domestic drama; her father’s death passes by in a blink, while the dying Lescaze lingers on for chapters. The author is eloquent, and exquisitely attuned to emotional nuance, yet it can feel uncomfortably intimate to watch her slow meander toward a sense of self, a perpetual rebellious adolescent coping with emotional challenges by, for example, visiting the piercing parlor or shopping. Lynn Darling’s sins may indeed have been necessary. This book was not—at least not for anyone but herself. And maybe that’s enough.

Alexandra Jacobs is features editor of The Observer.