SWEET TOOTH, by Ian McEwan. Doubleday, 304pp., $26.95.

A disgraced spy, a failed mission, a ruined lover: Ian McEwan's new novel, "Sweet Tooth," opens at full tilt.

Narrator Serena Frome is looking back to the early 1970s and a calamitous 18-month stint at MI5, the British intelligence agency. The pretty elder daughter of an Anglican bishop, she had studied mathematics despite being a bookworm at heart. When she graduates from Cambridge, her real education is just beginning.

All that summer, she pursues an affair with Tony Canning, an older, married professor who introduces her to pancetta, polenta and other sensual delights. Before dumping her, he sets her up with an interview at MI5, where he's rumored to have had a wartime career.

The title derives from the code name of Serena's first mission at MI5, which strives to fight the Soviets by sponsoring right-thinking and thoroughly unsuspecting writers. "This is a culture war, not just a political and military affair," Serena is instructed.

Masquerading as an employee of a generously endowed arts foundation, Serena duly signs up Tom Haly, a promising young author. He receives a monthly stipend, which gives him the means to dine out and fill his fridge with Chablis as well as turn down teaching jobs. Without realizing it, Tom becomes an agent run by Serena.

Inevitably, they fall in love.

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The novel's pleasures are multiple and, as always with McEwan, they begin with the storytelling. A faint word on a scrap of paper, the sense of being watched and an undelivered letter fuel Serena's suspicions about Tony's abrupt exit from her life and the reasons for her recruitment by the security service. Meanwhile, the "off-white lies" she must spin for Tom become a trap.

MI5 runs a staff lecture program, and Serena's notes provide a potted history of sectarian terrorism and a glimpse of a socio-economic backdrop in which unemployment and inflation are steep. This can feel forced, as if the novelist already had in mind the movie adaptation.

Quotidian details of life in 1970s Britain are more vivid. With miners striking and oil prices soaring, the government issues employees with insulating squares of felt to place between their feet and the cold floor.

There is insider wit here, too, including a cameo for Martin Amis and nerdy references to classic spy thrillers. Tom's stories recall McEwan's own early work, and the two share an editor in Tom Maschler.

These bookish preoccupations flag the novel's true concern, which is literature itself. The novelist, McEwan suggests, is the ultimate spy. While it's giving nothing away to say that MI5's attempt to influence fiction ends in fiasco, what of fiction's ability to influence real life?

"Sweet Tooth" champions just that. As its sly plot tells it, books not only promote empathy, they can even alter the course of a love story. If only this one didn't leave quite such a sugary aftertaste.