“The place was starting to get to me,” the narrator, a detective in Dublin’s fictional Murder Squad, says after seeing it for the first time, filled with the blood and corpses of its inhabitants. “Something about the holes in the walls, maybe, or the unblinking cameras; or about all that glass, all those skeleton houses staring in at us, like famine animals circled around the warmth of a fire.”

“Broken Harbor” is Ms. French’s fourth book, and though it is a psychological thriller with grisly murders to solve and troubled police officers to solve them, it is also a state-of-the-nation novel, a portrait of a wrecked Ireland consuming itself within. No. 17 on the New York Times best-seller list for Sept. 2, it has drawn praise for its elegant writing as much as for its clever plot. “She has irresistibly sly ways of toying with readers’ expectations,” Janet Maslin wrote of the author in The New York Times.

Interviewed recently in a hotel bar in downtown Dublin, Ms. French, 39, was soft-spoken, wry and still amused by her own success, which has come relatively late in a career she had never planned. She lives in Dublin with an actor and their 3-year-old daughter, but she grew up all over the place. Her father’s resource-management job took the family to Italy, Malawi and the United States, among other places. She wrote “your compulsory terrible teenage poetry,” she said, once had a short story rejected by The New Yorker and then abandoned fiction to become an actress.

But her dormant writer’s imagination woke up in 2002 when, resting between acting roles, she found a temporary job on an architectural dig near a large Dublin forest. “It was hard physical work — I wasn’t doing the little scrapy, trowelly thingie — and I started thinking, ‘What if three kids went in there to play, and only one came out?’ ” Ms. French said. She scribbled the idea on a phone bill, went off to play Feste in “Twelfth Night” and forgot all about it.

About a year later she found the bill and decided to expand the thought into a book, featuring a detective who is forced by the investigation to confront his own buried mysteries (most of which, tantalizingly or annoyingly, depending on where you stand, are never solved). The result was “In the Woods,” which procured Ms. French an agent, a two-book deal and a passel of prizes, including the Edgar Award for best first mystery novel by an American writer. (Ms. French was born in Vermont and has dual citizenship.)

Each of her books has been narrated by a different detective in the Murder Squad.

“I thought, I can do the conventional series thing where you follow the ups and downs of one character,” she explained, “or I can switch the narrators and save myself from the ‘Mousetrap’ syndrome, playing the same part for 10 years, and after a while you realize that you’ve been playing on autopilot.”

Ian Kern, manager of the Mysterious Bookshop in Manhattan, called Ms. French’s writing “phenomenal — not just in mystery fiction but in fiction in general.”

He added: “I like the way she plays around with these characters. As much as I like, say, Michael Connelly’s books, he’s got Harry Bosch in every novel, whereas these ones are more reminiscent of Ed McBain’s 87th Precinct books, with characters coming in and out.”

Ms. French’s second book, “The Likeness,” has a female detective go undercover to investigate the murder of a college student who is her virtual double. “Faithful Place,” her next novel, sends a detective back to his old neighborhood, where, among other things, he finally solves the mystery of what happened years ago to his vanished childhood sweetheart.

The narrator in “Broken Harbor” is a by-the-book detective named Mick Kennedy whose past plagues him as he gets caught up in a tricky mystery delving deep into a troubled family’s psychology. The idea came to Ms. French one evening when she saw a strange black shape scuttering across her kitchen counter and could not, at first, convince her partner that it was real. (It turned out to be a mouse.)

“What if it was happening while your relationship was already under strain, if you keep hearing this thing, and your other half questions your sense of reality?” she asked. In “Broken Harbor” Patrick Spain, a high-earning, high-spending husband and father of two, loses his job in the downturn, is saddled with a house he cannot afford and then becomes convinced that there some kind of evil animal inside its walls.

Ms. French said his descent into irrationality mirrored Ireland’s, in a way. “There was a national madness, a pure insanity,” she said of the country’s housing bubble, in which tens of thousands of families moved into ersatz new developments that are now falling apart. “These were supposed to be strong homes, fortresses against the world.”

Ms. French’s next book, she said, involves a strange case in which a photograph of a murdered teenage boy suddenly appears on a bulletin board at a girls’ boarding school, along with an anonymous note saying that the writer knows who killed him. The book explores, she said, “the tension, especially in teenagers, between the desire to keep secrets and the desire to reveal them.”

Though her books can feature murders, Ms. French’s interest, she said, lies not in “blood and gore and cruelty” but in something more interesting to her: the motivations and repercussions of murder.

“Murder — and the psychological implications around it — is, in a lot of ways, one of the biggest mysteries of the human mind,” she said. “Writing psychological mystery is a way to explore these huge mysteries that I’ll never actually understand.”