Sweet Tooth, By Ian McEwan

A beautiful blonde MI6 agent falls for an author she's sent to recruit – one who suspiciously resembles a young Mr McEwan

Serena Frome ("rhymes with plume"), the narrator of Ian McEwan's twelfth novel, is a beautiful blonde Oxbridge graduate who is recruited to MI6 in the 1970s and sent on a secret mission. We are told from the start that she was later sacked "having disgraced myself and ruined my lover"; the question, initially, is how and why.

As a kind of fusion of McEwan's own Atonement and William Boyd's Reckless, with an intelligence plot inspired by the CIA's secret funding of the literary magazine Encounter, Sweet Tooth plays with familiar tropes concerning writers as spies and liars. Serena, a bishop's daughter, is less of a natural spy and liar than Atonement's adolescent Briony Tallis, though her first serious love affair, which is with a middle-aged Cambridge don, involves adultery and deception.

Serena evinces a smugness about her comfortable background and being a Cambridge graduate that makes her repulsive, and she frequently teeters into parody when she exclaims at things being "so unfair!". Yet in the hands of an author as sophisticated as McEwan, her errors as an enthusiastic reader of fiction are more likely to shame the reader. As an undergraduate, our narrator jauntily informs us how she became a "trainee Cold Warrior" via contrarian opinions such as that "Valley of the Dolls was as good as anything Jane Austen ever wrote".

Her middle-aged lover, Tony Canning, offers her up to MI5 just before his death. Has he been assassinated? Is Maximilian, the awkward young man who is her superior at MI5, in love with her? Is her best friend spying on her?

Serena's education – sentimental, literary and political – becomes much more complex when she is sent to recruit a promising young writer, Tom Haley, with the offer of an annual stipend. First, she falls in love with his short stories; then with the writer himself. How long can she maintain her fictional cover story to the man who returns her passion?

Sweet Tooth takes the expectations and tropes of the Cold War thriller and ratchets up the suspense, while turning it into something else. What you see is not what you get, and the twist at the end reminds us of how many of this author's works, right from his early short story "Solid Geometry", confound readers' imaginations. Usually by involving the erotic. As in Atonement, the fact that one of its protagonists is a novelist alerts us to the trickery beneath its surface. But Sweet Tooth is also concerned with the point at which writing becomes political, rather than personal, propaganda.

Nevertheless, such excursions into the metafictional cause Sweet Tooth to become arch in a way which may irritate many readers. The novel's novelist, Haley, is suggestively close to the young McEwan – minus the support of the UEA creative writing course, the job at New Statesman and the smart boys' own club which helped rocket him to fame.

The publisher Tom Maschler and the authors Ian Hamilton and Martin Amis all appear in the story, the latter making audiences rock with laughter at a reading of his debut, The Rachel Papers, while poor Tom gets the dregs of their attention. (Amis buys him a triple scotch, however, and Tom still goes on to win an important prize. A novelist who does not win prizes is perhaps inconceivable to one loaded by so many.)

There are several evocative snap-shots of the grim, grey, strike-ridden decade of the Seventies, and Serena's Camden Town flat is suitably shabby and unpleasing. The psychological and period details build up, convincing us of veracity before jerking the rug away.But though this is his best book since Atonement, Sweet Tooth has none of the disquieting tragedy and dazzling technique of that novel, which remains perhaps the greatest in contemporary British literature. One doesn't care about Serena, or believe in her; she is carefully calculated to annoy, and her sexual self-confidence rings utterly false to a woman reader.

It's when McEwan, through his narrator, tells us that "Love doesn't grow at a steady rate, but advances in surges, bolts, wild leaps" that he touches us with something more than artfulness. If only this voice came through more clearly, and more frequently, with the truth drawn from experience, he would reach an altogether different level. This is why people still read Irène Némirovsky, after all.

Sweet Tooth, as expected, is a well-crafted pleasure to read, its smooth prose and slippery intelligence sliding down like cream. Yet one feels at the end that it is the prelude for a film script, with all the actors already cast, and its final question a foregone conclusion.

Amanda Craig's most recent novel, 'Hearts and Minds', is published by Abacus