Regarding the murder that lies at the heart of "Ocean State," the new Stewart O'Nan novel, the "whodunit" aspect lasts exactly 9 words into the book.

The first sentence of a story that takes place predominantly in Ashaway, Rhode Island, in 2009, reads: "When I was in eighth grade, my sister helped kill another girl."

It's a hell of an authorial gamble, and that O'Nan did so suggests he relished the challenge to shoulder significant weight in terms of developing characters and sustaining tension throughout the book after that opening detonation.

To that end, "Ocean State" isn't a typical thriller — if indeed it IS one. Two high school girls are infatuated with the same boy, a wealthy senior named Myles who, both women know (on some level), will graduate and head off to an elite college without a glance back. He casually and deceptively ping pongs between his beautiful longtime girlfriend Angel and relative newcomer Birdy, who has her own boyfriend but is willing to leave him for even a remote shot at Myles.

O'Nan, a New York Times bestselling writer whose other novels include "Last Night at the Lobster," "City of Secrets," "Henry, Himself," "The Good Wife" and "The Night Country," will read from and discuss "Ocean State" Thursday in Westerly's Savoy Bookshop & Cafe.

The jealous love triangle is not a particularly rare high school dynamic, and a scenario like "Ocean State" might be expected to continue without incident or even violence save for a chance photograph of Myles and Birdy that is posted to social media — which of course can turn even the most innocent image into a sort of Manhattan Project testing ground for emotional and spiraling gossip.

Angel can't handle the shame and mockery of this development as it pertains to her social and romantic standing at school — and particularly not in the context of Birdy, who, while certainly attractive, has nowhere near the cool reputation.

Simmering awhile

O'Nan's opening gambit might seem the sort of wild idea that occurs to a writer out of nowhere and in such tenacious fashion that an entire plot must then be created in support. But that's not what happened.

"The truth is, I'd been thinking about this story a long time," O'Nan says last week in a phone call from his home in Pittsburgh. "It's based on a terrible murder that happened in New Milford (in 1997). I kept trying to find my way into the story but I couldn't figure out how to approach it."

O'Nan, who lived with his family in Connecticut for several years and set several novels there, is referring to the death of 13-year-old Mary Ann Measles, who was bound, beaten, gang-raped and drowned by a group eight young friends who were angry the victim had slept with two of the men.

It's a horrifying scenario — all the more so because it's real — but O'Nan didn't want to recreate those details simply to craft a twisty contemporary crime novel. There were too many other aspects, he felt, that could be explored.

"Eventually, I thought of using Marie, Angel's little sister, as a narrator," O'Nan says. "It's a more interesting approach to use her perspective. What happens when your idol turns out to be a horrible person?"

Angel shares a room with Marie, a self-described "pudgy klutz" who idolizes and envies her sibling. The sisters move from one shabby residence to another with their divorced mother Carol, a good-hearted critical care nurse who loves her daughters but is sinking in a quicksand bog of increasing desperation over her vanishing youth and increasingly strained financial circumstances. This leads to a succession of boyfriends that require more and more of her attention.

Birdy is of similarly blue-collar circumstances, but her Portuguese family is devoted to one another and, through those binds, manages at least to stay on steady ground. That Birdy realizes this makes her ashamed she'd break up with her perfectly decent if predictable boyfriend for a cad like Myles — and yet she can't help herself.

Modern world

If the high school love triangle is a familiar scenario, it nonetheless feels unique and distinctive to its participants. O'Nan was intrigued by the depth of that reality, particularly now when we live in a culture obsessed with social media.

"I definitely wanted to explore the ecstasy and misery of young romantic love rather than familial," O'Nan says. "I had my cast of characters in a situation, and as I wrote, I understood them a little more each day. Utimately, I was able to connect with each of them. I don't think I was writing out of nostalgia because there's such a contemporary element. Social media is another set of eyes that is watching all the time. And in high school, where everyone is kind of performing for others all the time anyway, social media is all-knowing. That adds so much more of the pressure that kids are always trying to escape and avoid."

O'Nan describes buying a 2009 Westerly High School yearbook off eBay so he could familiarize himself with jargon, music and the overall aura of that slice of time for people of that age group.

"It gave me a bit of a window I needed," O'Nan says. "You know, to me and maybe people my age, 2009 doesn't seem like the past, but it really is a bygone era to the young people who lived it."

Sweet home Rhody

Another important element is the novel's evocative and heavily atmospheric portrayal of coastal Rhode Island setting, with which O'Nan has a bit of experience. "I wanted to set it in that part of Rhody because my wife's folks are from there and I've always found it fascinating. I also set it in a post-industrial mill town around Halloween because New England in the fall, with its long history and falling stone walls and cemeteries, is spooky country. There's always this sense of the past among the living."

Local readers will luxuriate in O'Nan's spare but beautiful descriptions of the area, including Misquamicut Beach, the abandoned mills, the strip malls and neighborhoods of Westerly and Ashaway, casinos and even a brief glimpse of New London.

Against this backdrop, the rippling dynamics of the murder on the families, the high school and a struggling small town are eerie. That everyone essentially knows what happened but continues to superficially carry on — even perpetrators Angel and Myles — is the disheartening stuff of contemporary society.

Points of view

This is all effectively captured as the narrative shifts from Marie's first person to third-person perspectives from Birdy, Angel and Carol, particularly as the inevitable crescendo draws closer.

But Marie's voice is delivered in a critically different sort of coming of age narrative in which the innocence of youth is dashed in a way that will leave her profoundly distanced from everything, even herself.

"Obviously, none of this is Marie's fault that it happened," O'Nan says, "and she stays with me. I find that's true, though, with a lot of my characters — and that's good. I can't tell why some books sell a lot, but the feelings I develop for the characters always stay with me.

"The best thing about reading or writing is to feel what others are going through. When you're feeling that as a writer, you get to feel it all day long for months. You just don't want to put the book down. That heat and warmth of being onto something is a real reward, and you hope other readers feel it, too."

If you go

Who: New York Times bestselling author Stewart O'Nan

What: Reads from and signs copies of his new novel, "Ocean State"

When: 6 p.m. Thursday

Where: Savoy Bookshop & Cafe, 10 Canal St., Westerly

How much: Free

For more information: www.banksquarebooks.com, (401) 213-3901