During the hazy summer months, the books we often tote—on vacation, to the pool, aboard a boat deck—are those that require sporadic attention. We’ve checked out until further notice, and desire a frothy escape, maybe even something we don’t mind leaving at the beach house for the next guests. But this year, the book poised to define summer 2015 and find its place in every bag is anything but a treacly throwaway.

Although Julia Pierpont’s hotly anticipated debut novel, Among the Ten Thousand Things (Random House), drops in the middle of beach-read season, the novel contrasts squarely against the expected. The book is an emotionally sophisticated, nuanced examination of a splintering Upper West Side New York City family, told over the course of a summer, with delicate peeks into the future throughout the narrative.

It begins with a bang: when a box full of correspondence between the family’s father, Jack, and his mistress arrives at his apartment, it falls into the wrong hands—the children’s. As the Shanleys unravel from this moment onward, their beauty and flaws are rendered masterfully by Pierpont: Jack, an artist whose vanity and pride scrapes the bottom of the barrel; Deb, an ex-dancer who can’t seem to figure out her place; 15-year-old Simon, reckless and aloof; and 11-year-old Kay, who should be an innocent bystander in her family’s tragedy, yet is at times too curious for her own good. It’s completely heart-wrenching and obsessively compelling. As Pierpont’s pages fly by, you’ll need to apply more sunscreen—you won’t be going anywhere.

“But what stays buried? Even heavy things have that way about them, of always coming to the surface—especially heavy things do,” Pierpont writes through Simon’s eyes. There’s a worldly intelligence to Among the Ten Thousand Things, as if written by someone decades older than Pierpont’s 28 years. It doesn’t necessarily follow that this is the novel that should arrive from a debut writer, sold at auction while she was still in an M.F.A. program—especially when so many others are churning out 600-page sci-fi epics with movie-franchise dreams, or looking for their place on the thriller shelves as the next Gone Girl; Pierpont’s approach has yielded a story poignant, fresh, and entirely her own.

I met the author on the steps outside Lincoln Center, near the reflective fountain, one unusually brisk June evening. Her mother, also a writer, had written for the New York City Ballet newsletter during Pierpont’s childhood. As we sat, crowds filed past for a New York Philharmonic show, Pierpont admits she wasn’t always so confident in her story.

“Starting the book, I was very reluctant to call it a book or commit to what I was writing about, because I was so afraid of writing about the wrong thing,” she says. “With your first book, there’s a lot of pressure to put everything in there.”

A teacher in her N.Y.U. M.F.A. program encouraged her to pursue the themes of infidelity that kept tugging at her, despite their unfamiliarity. “He just said to me, ‘Don’t worry about that, because you’re not going to accidentally spend all of this time and energy on something you don’t care about. You’re not going to accidentally write about something you don’t care about.’ It gave me this freedom to start anywhere.”

With the aid of famed novelist Jonathan Safran Foer as her thesis advisor, Pierpont plunged into the pages, the first of which were written for Zadie Smith’s workshop class. Foer taught Pierpont to set the bar as high as possible, asking her to imagine her writing as someone’s favorite story ever. “He’d say, ‘Just make it as good as you can.’ And it sounds so useless, but it’s not . . . I knew what he meant. It was weirdly helpful to have someone encouraging you to keep going and pushing you, even in the broadest sense.”