Ian McEwan is no longer a young man. This might seem obvious, but it needs saying if we are to make sense of where McEwan has gone with his writing. He was twenty-two when, in 1970, he enrolled on the University of East Anglia’s inaugural Creative Writing MA. The short-story collections that followed were brilliantly disturbing studies in the macabre and the perverse. Their impact was huge. Here was the imaginative flamboyance of Ballard, distilled into a taut, black, Pinteresque prose reinvigorated with post-adolescent brio. His early novels – The Cement Garden and The Comfort of Strangers – confirmed him, along with Amis and Rushdie, as the pick of his generation. And they are still there, all these years later, all in their fifties, their status apparently unassailable.

Why unassailable? Well, there is the theory that, in an age of celebrity-driven media, lazy literary journalism perpetuates the magnification of the Names at the expense of the Nameless. Or you could argue that no one has been excellent consistently enough to displace the Big Three. The bitchy, second-rate novelist in me leans towards the former view. And the not-them-again response of prolonged familiarity makes me wish they would make way for the next lot. But then I open the latest McEwan and I am almost always blown away by how good he is.

Even so, I worried lest Atonement should reaffirm a suspicion that the distance McEwan has travelled since his fledgling days has begun to tire him. Not least because it is, ostensibly, a novel about writing (a theme that is often the refuge of a bereft writer). His mouthpiece is thirteen-year-old Briony, who enjoys a privileged existence in Surrey in 1936. Prone to romantic reverie, she compensates for a lack of ‘secrets’ in her own life by inventing stories and plays for the amusement of her family. Already, she appreciates that the action of a plot is easier, if less satisfying, to depict than the subtler, stronger drama of the workings of the human mind. ‘It wasn’t only wickedness and scheming that made people unhappy, it was confusion and misunderstanding; above all it was the failure to grasp the simple truth that other people are as real as you … that was the only moral a story need have.’ This is where Briony’s writing must take her.

Unhappily, her search for emotional depth – in the creation of ‘real’ characters – coincides with her involvement in an actual emotional drama that she is too immature to comprehend. She spies on her older sister Cecilia stripping off and plunging into a fountain. An odd act, apparently performed for Robbie Turner, son of a cleaning lady and protégé of the girls’ wealthy father. Briony’s imagination hooks on to this incident, spinning the basis of a story from the fragile threads of what she has witnessed. Later, Robbie gets her to deliver a note to Cecilia; Briony reads the note, is shocked by it, and shocked again when she surprises the pair in the library. Her naive misinterpretation of what they are doing sets the scene for a far more grave and devious misrepresentation, one that will irreparably damage all their lives. Briony’s crime is not that she lies, but that she uses her gift for artistic fabrication to confuse fact and fiction. This strikes at the paradoxical heart of storytelling: that which is made up must be made to ring true. But for Briony, Robbie and Cecilia are not mere characters in a story; they are people. She realises this too late to avert catastrophe, but only at the end do we discover whether she can ever atone. The skill and compassion that McEwan invests in the unfolding of this tragic love story are exceptional.

For a tale told largely in monologues, in the words of teenagers and twentysomethings, the style is far removed from his punchiest early work. Not that this is a staid book, but it has a period feel and a tone of seasoned gravitas. What McEwan does return to here is the concealment of his undoubted intellect beneath the surface story. Since the mid-Nineties, he has tended to spell out his themes and ideas (Black Dogs, for example), rather than disclose them through the motivations, actions and interactions of his characters. It was as if the more he lived the more he felt compelled to pronounce on life. Enduring Love, despite its superb opening, and Amsterdam, despite the Booker Prize, manifested the proliferating symptoms of a writer at risk of being withered by age. (At the turn of the millennium, which modern author would have wished to be compared – as he was – to Huxley, Chesterton and Henry James?) But just as I’m beginning to despair of rekindling my flame of admiration for Ian McEwan, he rediscovers his vitality in the guise of a girl four decades his junior. Isn’t youth a wonderful thing?