Over the course of a year, Dani Shapiro committed countless hours to “The Virtual Dementia Tour,” a personal essay contending with her “obsession” as a writer: memory and time.

“I had struggled with it, finally cracked it, and was feeling really good about what I’d written,” says the acclaimed memoirist and novelist, whom Kirkus reached by phone at home in Connecticut.“Then I woke up the next morning in a state of horror, with the realization that it wasn’t an essay—it was a book—and it was about marriage.”

Furthermore, it was about her marriage. “The Virtual Dementia Tour” hinged on an experience Shapiro shared with her husband and frequent collaborator, Michael Maren: the pair was hired by a pharmaceutical company to write a play intended to foster empathy for Alzheimer’s patients. It was performed on a corporate retreat, during which they volunteered for the Virtual Dementia Tour (actual name), a simulation devised by a geriatric expert.

Participants were required to wear spiked sandals, scratched goggles, massive headphones, and several pairs of surgical gloves to complete a series of five tasks.

“Quite a number of us became frustrated or angry,” Shapiro writes in Hourglass: Time, Memory, Marriage, the book the essay begat. “A few, like me, gave up. But there is one man the researcher focuses on. This man broke the rules. He insisted that the list of tasks be repeated until he was sure he had heard them all.”

In a triumphant finale, “he switched the flashlight on—my husband—and raised his fists in victory.”

For Shapiro, their disparate reactions to the experience illuminated significant truths about their relationship.

“That was where I hadn’t gone in the essay,” she says, “and it was, unsurprisingly, the place that was most terrifying—the idea that I was compelled to write about a relationship that I’m deeply inside of, am quite fond of, and don’t want to damage in any way.”

Shapiro is the author of eight books, including the bestselling novels Black & White and Family History and the memoirs Still Writing, Devotion, and Slow Motion. Her work has appeared in the New Yorker, Granta, Tin House, One Story,and Vogue, among others. She has taught at Columbia, NYU, the New School, and Wesleyan University. With her husband, she co-founded the Sirenland Writers Conference in Positano, Italy. They live in Litchfield County, Connecticut, with their teenage son.

“As a memoirist,” she continues, “the idea that I would be willing to reveal various complex and [even negative] aspects of myself is something I’m aware of the necessity of, that I have a certain comfort level in doing. But when it came to...my husband and the idea of pulling back the curtain on us—there’s a reason why people say you never really know what goes on in somebody else’s marriage.”

Hourglass: Time, Memory, Marriageis a dispatch from the front line of Shapiro’s 18-year marriage to Maren (“M.” in the book), a former war correspondent–turned–lover, husband, and father. The marriage is Shapiro’s third. Over its course, they share successes and failures, passion and profound loss. They have patches of perfect synchronicity; sometimes, she looks at him and sees a stranger. They grow older, wiser, wearier—together.

“I’ve become convinced that our lives are shaped less by the mistakes we make than when we make them,” Shapiro writes in Hourglass. “There is less elasticity now. Less time to bounce back. And so I heed the urgent whisper and move with greater and greater deliberation. I hold my life with M. carefully in my hands like the faience pottery we brought back from our honeymoon long ago. We are beautiful. We are not new. We must be handled with care.”

Hourglass is careful yet incisive—an inquiry—with brutality as well as beauty in the telling. (“I hated him,” Shapiro writes of one charged moment.)

“I wanted to try to capture the complexity, the disappointment, the imperfection that goes along with being with someone over the duration, but, more than anything, I wanted to capture the beauty of it,” she says. “Those things are not contradictory. They’re not oxymoronic. They are part of living with someone who sometimes disappoints you or who grows at a different pace or rate. It’s being able to, in the fullness of time, say, This is it—nobody’s going anywhere.”

Shapiro employs wise words of elders and sages to expand on her observations of commitment, feathering the nest of the narrative with quotations from writers, philosophers, scientists, family, and friends. Thoughts on relationships and the ravages of time range from Rilke’s (“Let everything happen to you: beauty and terror”) to a paraphrase of Grace Paley, who likened the duration of the decades between 50 and 80 not to minutes but seconds.

“There are people who have walked this road before me,” says Shapiro, whose long-term practice of keeping commonplace books—small notebooks where one may collect aphorisms, ephemera, etc.—naturally fed into her project. (She invokes Don Hall and Jane Kenyon, Mary Oliver and Molly Malone Cook, and Joan Didion and John Gregory Dunne as helpful guides in contemplating marriage between writers. “I don’t think I could have written Hourglass if M. were not a writer,” she adds.) “There was no one that I quote in Hourglass that wasn’t already in some way or another part of one of my commonplace books, someone I’d gone to for wisdom or for solace. And I wanted the book to be able to be read, in a way, as a commonplace book of marriage.”

Her original contributions to the triptych of contemplation—time, memory, marriage—are as memorable as any she quotes.

“Our world will narrow as the storm of time washes over us,” she writes. “It will bleach us, expose our knots, whittle us down like driftwood. It is this narrowing—not uncertainty—which is inevitable. The narrowing will not happen today, nor tomorrow. Not this year, nor next. Not this decade, nor—perhaps—the one after. There is luck involved, of course. But not only luck.”

Megan Labrise writes “Field Notes” and features for Kirkus Reviews and is the co-host of the Kirkus podcast, Fully Booked.