Over the last 12 years Tana French has become known for blisteringly good crime thrillers narrated by various cops in the fictional Dublin Murder Squad. As so often in crime novels, they tended to be outsiders in some way, or struggling with their own past trauma. For her seventh book, she has created something rather different: a pin-sharp portrait of privilege, recounted not by a world-weary, wisecracking detective but by a crime victim who is also a suspect.

Twentysomething Toby has led a charmed life: popular at school; rich, supportive parents; sweet, adoring girlfriend. He bagged his first job doing PR for an art gallery – fortunately, the boss “had taken a chance on grass-green me when the other woman at the final interview had had years of experience”. Worrying has always seemed “like a laughable waste of time and energy”; after all, he’s never had anything to worry about. And then an overconfident bit of trickery at work is followed by a brutal attack in his own home, and the old Toby is gone for ever, replaced by a nervy, jittery wreck with a limp and a slur who gets lost in the middle of sentences.

As well as the fear and the “roiling fury”, he’s left with “a depth and breadth of loss that I had never imagined”. French writes excellently about damage, both physical and mental, and the accommodations that need to be made when life takes a wrong turning. Toby is not the only one with changed horizons; his uncle Hugo has been diagnosed with terminal brain cancer, and Toby goes to stay with him in the family pile known as the Ivy House, where as a teenager he spent summers with his cousins Leon and Susanna. Hugo deteriorates while Toby struggles to recover; the house becomes a haven for them both, even if “my own ghost was everywhere … agile and golden and invulnerable”.

We are a third of the way through before the grisly discovery in the Ivy House garden that sets the book’s central mystery in motion and brings the police to Toby’s door for the second time. “Inside, what, five months? You’re burglarised, you’re nearly killed and a skeleton turns up in your back garden? What are the odds?”

Slowly, with infinite cunning, French teases out the connections. The old Toby would have faced down the cops with patrician charm; the new one doubts himself, his past, his memories. The attack has left him with “holes in my mind, blind spots shimmering nastily like migraine aura”. He’s taking Xanax for the anxiety, he’s certainly an unreliable narrator – as are we all. As the book unfolds he is forced to confront the blind spots that were there before the burglary: how the blessings of birth and class and gender have insulated him all his life, from teenage bullying, from toxic masculinity, from social oppression. “Oh you,” says Susanna, almost fondly. “Anything you feel bad about just falls straight out of your head.”

Though both the reader and Toby are tripped up at every turn as he searches for what he might have forgotten, some of the best passages follow not the excavation of the mystery but the awful development of Hugo’s illness. French ranges effortlessly from pub banter to moral argument to visionary intensity, with the present tense erupting into the narrative – “my feet thumping on the ground, my breath loud in my ears. Waves of birds lifting from the trees” – just as the past erupts into the present day. Hugo is a genealogist: his own investigations have been transformed by modern DNA techniques, and a subplot highlights the shocks in store for people investigating their family trees who discover that they are literally not who they thought themselves to be.

Throughout, there’s a bittersweet appreciation of the fragile beauty of the world, from “the sunlight bringing the battered wood of the table alive with an impossible holy glow” to the garden that sheltered childhood memories as well as a timebomb waiting to be unearthed. The novel is saturated with yearning, for vanished and vanishing worlds, as Hugo goes down into the darkness and Toby faces up to the scale of his loss. That what he is mourning was in part a chimera created by privilege – “not everyone gets to live in the same world as you” – is just one layer in the book’s overlapping ironies.

So the novel works brilliantly as a twisty pageturner, but it is far deeper and more nuanced than that. French’s theme throughout is the bruised relationship between the world and the self: whether our personalities are remade by trauma, or revealed; what is concealed by privilege, and what is exposed. As Hugo says, “one gets into the habit of being oneself. It takes some great upheaval to crack that shell and force us to discover what else might be underneath.” That “great upheaval” is the modus operandi of the best crime fiction, and this book confirms French as its brightest contemporary star.

• The Wych Elm is published by Viking (£14.99). To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.