I KNOW who killed him - but I'm envious of anyone who does not, because it means they have yet to read the new novel by the bestselling, multiple award-winning Irish author Tana French, already acclaimed as "one of the finest crime writers in the world".

Although I would argue that her intelligent, atmospheric, luminously written work transcends such genre pigeon-holing.

The Secret Place is terrific - I read its 518 pages in about three sittings, infuriated by the intrusion of real life - so I have no intention of spoiling its mysteries, although it is French's lyrical writing, as well as her portrait of the ferocious emotional landscape of teenage girls, that is so mesmerising.

A confession: I'm not a crime fiction buff, but I'm not alone in my admiration for her latest book. Gillian (Gone Girl) Flynn, Kate Mosse and Sophie Hannah also know who killed him, as does Stephen King, who has tweeted of The Secret Place, "It's terrific - terrifying, amazing, and the prose is incandescent."

French, who is married to actor Anthony Breatnach, with whom she has two small daughters, confesses that she almost incandesced physically when she first heard of King's compliments about her fifth novel, which again features members of Dublin's Murder Squad, some of whom we've encountered in French's previous novels. "I couldn't believe it," she says of King's encomium, admitting to pinching herself lest she were dreaming, when we talk in the bar-cum-library of one of Dublin's most venerable hotels.

Ironically, as we begin the interview, the clangour of police sirens pours in through open windows. She was an actress in her previous existence, so has she perhaps engineered the soundtrack of the Dublin Murder Squad swinging into action?

"No," laughs French, who is petite and fine-boned, with a beautiful, low speaking voice and a lilting Irish accent. "There is no such small unit in the city police force, it's fictional." As is St Kilda's, the exclusive Dublin boarding school that's the setting for The Secret Place, which begins when Holly Mackey, the 16-year-old daughter of undercover police officer Frank Mackey, takes a photograph and a story to a young, ambitious detective, Stephen Moran.

He has not seen Holly since she was nine years old, when she was a witness in a murder investigation in Faithful Place - French's third novel, of which Sara Paretsky wrote that the relationship between Holly and her father was "a small masterpiece."

Holly tells Moran she found the photograph on a card pasted on a school noticeboard - the secret place of the title - where girls pin up their secrets anonymously. It's a picture of 16-year-old Christopher Harper from the posh neighbouring boys' school, who was found murdered in the grounds of St Kilda's a year earlier, a crime that remains unsolved. The caption with the photograph reads: "I know who killed him."

Told over the course of one day, the story switchbacks effortlessly between past and present, third and first person, as Moran tries to solve the murder while working with a hard-bitten female detective. But it's 40-year-old French's ability to recall so vividly the raw, jangled experience of adolescent girls, with their crackling energy, gangling limbs and smart-mouthed attitude, that is so astonishing.

Then there's the febrile, hormone-saturated, angst-ridden world of St Kilda's, where Holly and best friends Becca, Julia and Selina are boarders. The place is riddled with rumour and rivalry. As for the feverish friendships, "I think those teenage friendships where you swear eternal bonds shape you, they create you. Adolescents are so fierce," says French, who got the idea for The Secret Pace after being sent a link to the website, postsecret.com, an ongoing art project where secrets are told anonymously on the back of postcards. "They go from dark, moving stuff to the silly. We all want to reveal our secrets but we also want our privacy to be inviolate, so I began thinking about adolescents' desperate need to have secrets - and to share them."

So, what sort of teenager was the Vermont-born novelist, who has dedicated her novel to four school friends from the international school she attended in Italy and "who luckily were nothing like this. Thank goodness!

"I was certainly not a handful. I spent a lot of time writing really, really awful poetry, which I hid under the bed. I think the intensity of being a teenager is the same everywhere, although I chose to set the novel in an elite boarding school because the pupils are so sheltered; it's the classic enclosed community. I was educated at a number of schools - none of which was anything like St Kilda's," she replies, adding, with a sly wink, that she saved all her bad behaviour until she got to Trinity College, Dublin, where she studied acting.

Her mother, Elena Lombardi, is a translator and interpreter. Her Irish-American father, David, worked in international economic development, so French and her brother grew up in America, Italy, Ireland and Malawi. It was when they began spending time in Ireland that she knew she'd found her special place, although she retains dual US and Irish citizenship. "I can't claim to be Irish or from Dublin but it's the city I know best after all that travel. I think you learn a lot as an outsider, you observe everything more closely."

She's always loved words, recalling her father reading Kenneth Graham's Wind In The Willows to her at bedtime when she was six years old. She was dazzled by the beauty of the language - "the description of a river, 'that sleek, sinuous, full-bodied animal.' I had no idea what sinuous meant; I just fell in love with the word. I'm still a sucker for beautiful writing. I desperately wanted to become a writer as a child. Then I thought I'd study archaeology and discover Troy, until I found out someone had got there ahead of me."

Instead she became an actor. While "resting" between jobs she helped on an archaeological dig outside Dublin - "it's rather like being a detective" - next to woodland. "I kept thinking it was a wonderful place for children to play. I also thought, 'What if three children went into the wood and only one came out?' I wrote the idea down on a scrap of paper, then went off to play Feste in Twelfth Night. I forgot about it until we were moving and I found the note. I began writing, though I'd no idea whether it was any good."

That scribbled note turned into her first novel, In The Woods (2007). A huge bestseller, it won numerous awards, including an Edgar for best first novel. Two more bestsellers followed, The Likeness and Faithful Place. Her fourth, the terrifying Broken Harbour, is another "what if" story, about the descent of a mind into insanity.

One evening, she was at home writing and her husband was despatching zombies on the Xbox. She went into the kitchen and out of the corner of her eye saw a dark shape moving across the work surface. Her husband couldn't find anything, putting it down to her overactive imagination, "which, thankfully, pays the rent". French was disquieted to have seen something someone else hadn't and that she'd not been able to prove it. It later turned out to be a mouse, but she began to think what would it would be like if this happened to someone whose world and home was already under threat, under attack from outside or inside.

Additionally, she had been thinking about Ireland's "ghost estates" of unoccupied or abandoned houses left after her generation was lured into buying homes on half-built estates because it was alleged that there was going to be a property boom; then the Irish economy went into meltdown. "I desperately wanted a house, but we couldn't afford a shed. We were a couple of very broke actors - it was literally, 'Can we afford milk or toilet rolls'," she laughs.

Being an actor - she'd like to go back to performing one day - is a huge advantage for a novelist, she confesses, since she was trained to put herself into other people's shoes. "I was taught how to create a character as a three-dimensional person and that helps to sustain imaginative worlds, filling them out, drawing people into the character's life and making them feel their fears," she explains.

A long-time fan of crime fiction -particularly of Josephine Tey, Donna Tartt and Sophie Hannah - she never knows whodunit when she starts writing. "With Broken Harbour, I was almost a third in when I worked it out. I had to go back and do all these rewrites. I can only get to know the characters by writing them. It's a pain!"

There is no blood or guts in French's novels. "My books are not classic whodunits. For me, the whydunit is far more interesting. I like atmospheric crime novels rooted in a society, a time and a place, exploring the ripples of what happens around a murder, with many lives destroyed.

There's no loving detail in my books such as, 'Then he pulled her fingernails out with a pair of pliers.' I'm not concerned with evil. I much prefer an archaeological dig into the human mind.''

The Secret Place by Tana French is published by Hodder & Stoughton, £14.99