McPhee’s parents — the writer John McPhee and the photographer Pryde Brown — divorced when Martha was 4 years old. Martha and her three sisters went to live with their mother and her boyfriend, a larger-than-life figure named Dan Sullivan, who cruised into their lives in a turquoise-colored Cadillac wearing a cowboy hat.

Sullivan had five children, Pryde brought her four daughters, and together they had one more baby. The whole clan settled at Omega Farm, a hunting lodge turned home on 45 acres of New Jersey forest, about 30 miles from Princeton.

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Life there was chaotic, with most of the trouble stemming from Sullivan: An unlicensed Gestalt therapist, he met his clients in Omega Farm’s indoor swimming pool, everyone buck naked. He hauled the family to Big Sur, Mexico and Haiti. He spent evenings sitting on top of the barn, passing a joint around to the kids. “It was the seventies, after all,” McPhee writes.

Pryde romanticized the family’s unusual lifestyle, wanting her daughters to see the on-the-edge moments — “making it on empty to a gas station in Guadalajara, escaping catastrophe and banditos” — as adventure. But McPhee remembers her mother “driving with my sisters and me late into the night in our old beat-up green station wagon, trying to decide if she should leave my stepfather or not. He had a temper, had hit her, had caused her to get stitches and suffer a concussion.”

Perhaps ironically for McPhee’s story, Gestalt therapy focuses on the present, not the past, but McPhee — a novelist whose books include “An Elegant Woman,” “Gorgeous Lies” and “Bright Angel Time” — is wise enough to realize that you can’t understand one without the other.

About a third of the way through the book, her narrative takes a sharp turn when she reveals that she was sexually molested by Dan at Omega Farm when she was 11. Twenty pages later, the narrative takes another turn as McPhee moves the story back into the present to describe the hard work of caring for her mother and restoring the damaged forest surrounding the house. (John McPhee pops up now and again, delightfully, stealing the scene each time. When Martha asks if she can borrow his pickax, he corrects her: “‘It’s a pick mattock,’ he said, and explained the difference.”)

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As the pandemic eases, Martha McPhee begins, stubbornly, to improve the farm, hacking out overgrown bamboo and repairing a broken septic system. One job leads to a bigger one, and then to a bigger one, and finally to a job that is larger than anyone can handle: restoring the forest and its understory, which has been devoured by an overabundance of deer and smothered by invasive plants.

It’s clear that for McPhee, repairing the forest is symbolic of repairing her family. It’s also clear that both are impossible tasks. “My need to repair and renew was urgent, desperate,” she writes. “My mother had messed up a lot. I couldn’t have put it so concretely in the moment, and in that year in New Jersey I often wondered what I was doing there — but I would come to see that my fear of leaving was inextricably bound to my desire to understand what had happened, and to make it better.”

McPhee’s prose is steady, her tone thoughtful. She examines events of the past from all angles. She is amazingly generous, loving her mother deeply, even as she wonders, years after Dan’s death: “What did she know and when? … Why did she stay with Dan when she knew? Why did she ask us to love him?”

She examines her own feelings: The molestation provoked shame, fear and embarrassment, but also a brief instant of pleasure. “At first, I didn’t want this to stop,” she notes. “I am ashamed to say that, even now.”

Throughout, McPhee corrects her own memory repeatedly. She walks right up to telling the reader something about someone and then stops, noting that it is not her story to tell. This carefulness adds to her credibility; she positions herself neither as victim nor saint but as someone who, she says, only wants to be good.

“It isn’t possible to fix this family,” she notes. “It was broken and reimagined a long time ago. Fixing it was never my job.”

And yet, pick mattock in hand, she marches into the thicket to hack away at the past.

Laurie Hertzel is a book critic in Minnesota and the author of the memoir “News to Me.” She teaches in the low-residency MFA program at the University of Georgia.