Unless their protagonists are of the unflappable James Bond mold, novels of the spy genre often feature idealistic and empathic characters becoming cynical and emotionally jaded after one bout too many with a cruel and pitiless world. In Sweet Tooth, Ian McEwan (acclaimed British author of award-winning novels such as Atonement, Solar and the Man Booker Prize winner Amsterdam) forgoes this tack, choosing instead to have the story’s two protagonists stubbornly cling to the possibility of love despite their increasing world-weariness.

The result is winsome and heart-warming, if somewhat cheery. Sweet Tooth is narrated by Serena Frome (“rhymes with plume”), who recounts her experiences as a young and low-level functionary in MI5, Britain’s domestic intelligence agency, years ago. McEwan transports the reader to 1972-’74, peppering the story with references to coal-miners’ strikes, the OPEC oil embargo, fuel shortages, and the double-edged sword of newly attained and heady social freedoms.

Feminism is in the air, too — though it’s not quite ubiquitous. Of women in MI5, Serena observes, “[M]ost of us (I exclude myself, of course) were the mistresses of the lowered gaze and the compliant near-smile.”

Sweet Tooth initially feels like light reading: Serena is a headstrong but vulnerable ingenue struggling to understand why her older educational and professional mentor abruptly terminated their affair. She strives to overcome workplace misogyny and yearns for true love. But gradually, confidently, McEwan steers the story toward substance.

Fulfilling her maiden mission, codenamed “Sweet Tooth,” Serena convinces Tom Haley, a young writer critical of communism, to accept funding from a literary foundation. Unbeknown to him, the foundation is a front for MI5. Serena’s superiors hope that with time and money, Tom will (unbidden) produce anti-communist fiction reminiscent of Orwell. Meanwhile, a smitten Serena mines Tom’s short stories for his views on women and relationships. His fiction continues to captivate her even after they become lovers. “I became uneasy whenever one of his male characters became intimate with a woman, with another woman,” she admits.

McEwan explores complex and profound themes here, such as patriotism’s proprietary attitude toward culture, and whether fiction can reveal its author’s nature. He also deepens Serena and Tom’s relationship; she agonizes over how to tell the man she loves that she has deceived him.

Spy novels often boast plenty of twists but few real surprises. Sweet Tooth, however, includes a plot development at once unpredictable and plausible. Such is McEwan’s dexterity in crafting this game-changer, that not only does it mesh with the story but also enrobes what came before with an extra layer of meaning. To be sure, the delicious ending reinforces Sweet Tooth’s slightly-too-sunny disposition, but it is difficult to remain impervious to the story’s life-affirming and almost defiantly romantic outlook.

Rayyan Al-Shawaf is a writer in Beirut.