Ian McEwan, author of Atonement and Amsterdam, which won the Booker prize in 1998, knows how to begin a story. Sweet Tooth has your attention from the get-go:

My name is Serena Frome (rhymes with plume) and almost forty years ago I was sent on a secret mission for the British security service. I didn’t return safely. Within eighteen months of joining I was sacked, having disgraced myself and ruined my lover, though he certainly had a hand in his own undoing.

So this is a love story involving a secret agent, but we must wait. The love story does not begin until midway through the book. First we must let Serena recall her school days and undergraduate life in Cambridge, where she has an affair with a history professor. It is he who recommends her to MI5. This is the early Seventies, the height of the Cold War, when not only soldiers and secret agents but also writers and intellectuals were ranged on opposing sides, defending communism or democracy.

Serena’s bosses hear of her love for books, so she is assigned Operation Sweet Tooth. She has to approach a promising English writer, who has been writing against the communists, and offer him money from a foundation so he can continue writing instead of having to look for a job. But she must not tell him she is a secret agent and that he will be actually funded by British intelligence.

Such things did happen during the Cold War. The highbrow monthly magazine Encounter was eventually revealed to be funded by the CIA.

Serena is successful in her mission. The writer, Tom Haley, who has been doing a doctorate at a redbrick university, accepts her offer. But the operation does not go entirely according to plan – they fall in love. Serena, however, does not tell him she is working for MI5, which is working behind the scenes to make him a famous writer. His first book is published and wins an award. He becomes a celebrity overnight. But then there’s a leak. Operation Sweet Tooth is exposed. The Guardian reports Haley is being funded by MI5.

Haley issues a statement saying he did not know he was being paid by MI5. Serena cannot look him in the face. She feels guilty for not having told him she worked for MI5.

But he knew, he knew, she later learns, and has gone on loving her. She makes the discovery when against the advice of her bosses, who tell her to break off contact with him, she returns to their flat and finds him gone. He has left a letter for her. It tells her how he learnt her secret, his initial bitterness, and why he had not broken off their relationship.

He still wants her if she will have him, he writes. Those are the last lines of his letter:

Tonight I’ll be on a plane to Paris to stay with an old school friend who says he can give me a room for a few days. When things have quietened down, when I’ve faded from the headlines, I’ll come straight back. If your answer is a fatal no, well, I’ve made no carbon, this is the only copy and you can throw it to the flames. If you still love me and your answer is yes, then our collaboration begins and this letter, with your consent, will be Sweet Tooth’s final chapter.