The first-person narrator of “The Bullet,” Mary Louise Kelly’s thriller about long-buried family secrets and the limits of self-knowledge, could not be further removed from either the pistol-toting pulp-fiction dames who gave rise to the femme fatale, or from their scantily clad granddaughters.

Or so it seems at first.

Caroline Cashion is a French literature professor at Georgetown University who uses words such as “stodgy”and “spinster”to describe her life. Bespectacled, close to her parents and fond of evenings spent sipping tea in her favorite library nook, she is certainly no Lara Croft, as she cautions us in the novel’s opening paragraph. Sure, she shares the avatar’s long dark locks, hourglass figure and liquid brown eyes, but to borrow from another character’s observation, Caroline is more akin to sultry TV chef Nigella Lawson. Here is a woman with passions that her current way of life is failing to satisfy.

This self-declared “unlikely heroine” is about to be sucked into the heart of an unsolved double homicide dating back to the 1970s. Turning sleuth and then hungry vigilante, she eventually will be juggling blond wigs, unwinding duct tape and packing a .38-caliber Smith & Wesson. As she sums herself up, “You think you know someone. Then, at the age of thirty-seven, you grow up.”

It’s Caroline’s very conscientiousness that provides the catalyst for her transformation. When sharp pains begin shooting through her wrist, her doctor blames too much typing. She’s given an MRI, and what that image reveals upends her life. In the back of her neck, lodged alarmingly close to her spine, is a bullet. She has no idea how it came to be there.

"The Bullet" by Mary Louise Kelly (Gallery Books) (Gallery/Gallery)

Demanding answers from her parents, she learns that she was adopted at age 3. And there’s more to come. Her birth parents were murdered, shot at close range in their Atlanta home. Nobody was charged with the crime, and there was only one eyewitness: a terrified little girl who’d been left for dead.

That child was, of course, Caroline, and while she may not be able to recall anything of that fateful afternoon, she has been carrying in her body a crucial piece of evidence. With surgeons now keen to remove it, it’s of interest not only to the detective who investigated the crime but also to the killer. As Caroline races to find him before he can find her, it’s no wonder that she has what she calls “Ingrid Bergman” nightmares — grainy bad dreams characterized by “a long buildup, tension ratcheting scene by scene.”

“The Bullet” has an ingeniously simple premise, and the confounding, downright creepy aspects of Caroline’s predicament are amply engaging. Questions of destiny and justice add depth, and there are some pleasingly menacing metaphors. “The more I tried to catch it, the more it eluded me, like a kitten batting a piece of yarn,” Caroline says of her sense that something isn’t quite right.

Although Caroline characterizes her romantic interests chiefly by their style of jeans, the novel conjures up a bevy of strong women, among them Caroline’s Georgetown boss, an imperious Frenchwoman with a secret passion for thrillers. If only Caroline had picked up one of those Jack Reacher books, I found myself thinking, perhaps then she’d have wised up a bit sooner to what goes on in such plots. As it is, she’s just a little too slow to catch up, resulting in a novel that is at least two-thirds buildup, and sometimes drags despite a backdrop that shifts from Washington to Atlanta to Nantucket, then to Europe.

Really, though, this is as much a portrait of metamorphosis as it is a thriller, and it owes less to the likes of Lee Child — or Alfred Hitchcock — than to Albert Camus. “She bored me,” Caroline says of her old risk-averse, introverted self. By the novel’s close she has become an avenging femme fatale, and if there’s something a touch jarring — faintly implausible, even — about that transition, it serves to crank up the unease and make her seem more of a loose cannon. You’ll finish this book knowing whodunit and why but with a refreshingly unresolved sense of how Caroline’s own story will end.

Anderson is a freelance book reviewer and the author of “Chastened,” a memoir.