SWEET TOOTH. By Ian McEwan. Doubleday. 324 pages. $26.95.

Serena Frome, the narrator of Ian McEwan’s 13th novel, “Sweet Tooth,” is something new in the McEwan annals: a hero who verges on caricature. She’s a bombshell (“sleek and fair”) with a steel-trap mind (“I knew the answers to questions before I even knew how I got to them”). You’ve seen her strutting through spy romances, and “Sweet Tooth” is, on the face of it, just that: a spy romance.

Serena Frome is a low-level recruit to MI5, tapped while studying math at Cambridge. The year is 1972, a “golden idyll,” at least as she remembers it 40 years later. In the opening paragraph, we learn that she was sent on a secret mission, bungled it and left in disgrace. “I didn’t return safely,” she confesses.

But this is Ian McEwan, a playful novelist whose narrative control is legendary. The straightforward rise and fall of a self-described “office girl in a mini-skirt” might be fun to read, but it’s not that fun to think about.

McEwan has written a novel whose subject is trickery and whose core actions are grounded in tricks. The push and pull of who owns the truth, still playing out in the dying days of the Cultural Cold War, infiltrates all aspects of the novel.

McEwan introduces layers of watching with potential misreads at every level. Serena Frome is a professional spy trained to watch, interpret, and report. She’s also expected to fabricate an identity and fudge the truth. Her prime target, when she’s finally moved into an intelligence operation, is Tom Haley, a watcher and fabricator of a different sort. He writes short stories.

Serena, the 2012 narrator, is re-creating her own younger self.

So is McEwan resuscitating the writer he used to be in Tom Haley? They share a writing style, a university (Sussex) and even a publisher (Jonathan Cape) and editor (Tom Maschler, who discovered Mc-Ewan).

McEwan also borrows the premise for “Sweet Tooth,” Frome’s intelligence operation, from real life. In 1966, American reporters discovered that the CIA had funded “Encounter,” a high cult magazine. The CIA’s reason for a secret operation amused McEwan: They wanted to show off the products of a free society. Scaling back a bit, he imagines that MI5 has decided to support 10 writers. In yet another twisty move, Tom Haley writes a novel, “From the Somerset Levels,” a gift from McEwan, who published it in “Encounter” magazine in the 1970s.

So what’s behind these fact/fiction links besides an author winking at us and playing metafictional games? There’s something delightful about the way McEwan undercuts his own serious intentions, as if he’d turned the grave implications of “Atonement” upside down. “Sweet Tooth” is a love letter to reading and writing.

Serena begins to fall in love with Tom as she reads his work, but she misses the point that Tom will be her match in duplicity. His stories imagine strange conditions of imposture and proxy emotion: A man gives a sermon in place of his twin brother, a vicar. While in disguise, he becomes the object of love for a woman who will train him to her will.

Another begins with a dull fellow who passes some mannequins in a store window. One of them seems to be standing apart, having a private moment. He buys her, along with some expensive dresses, and installs her in his mansion. Predictably, things go downhill. The experience, says McEwan, “bequeathed him nothing.”

A talking ape narrates another story. The punch line reveals that the narrator is really a woman and that the ape is just a “spectre ... of her fretful imagination.”

Serena is both tantalized and annoyed. She reads to encounter reality and is not impressed by “those writers who infiltrated their own pages as part of the cast, determined to remind the poor reader that all the characters and even they themselves were pure inventions.”

No room in the books she likes for the “double agent.” McEwan is, of course, a double agent, constructing a world that the last chapter deconstructs. It’s possible to read “Sweet Tooth” as two books: the one you open innocently and the one you rediscover after the final twist. Try it.

Reviewer Catherine Holmes teaches English at the College of Charleston.