Although Alice LaPlante’s gripping first novel, “Turn of Mind,” is narrated by a suspected killer, don’t expect to be given any privileged information by the protagonist. Jennifer White, the retired orthopedic surgeon who might have brutally murdered her best friend, suffers from an advanced case of Alzheimer’s. While the Chicago police and her family strongly suspect that White is guilty, to be certain they need her to account for her actions at the time of the crime. And the inexorable creep of dementia makes that increasingly unlikely.

The circumstantial evidence against White is strong. The victim, a retired teacher named Amanda O’Toole, was her closest friend, but they had a contentious relationship that occasionally descended into vicious fights. White had ample opportunity to commit the crime, since the two women were neighbors who had free access to one another’s houses. The most damning piece of evidence is the gruesome nature of the murder itself. Although O’Toole died from a blow to a head, four fingers on her right hand were neatly severed soon after the killing. And White’s medical expertise is in hand surgery.

While it is tempting to see this as an open-and-shut case, LaPlante skillfully sows enough doubt to keep us guessing. The victim was not without enemies. She was a malignant busybody, a seducer who was out to snare personal secrets, not sex. She saw herself as “truth’s vehicle,” a sort of ethical enforcer who aggressively confronted those around her about their perceived shortcomings. There is even a suggestion that she planted pornography on a colleague’s computer after deciding he was a bad influence on his students.

Both of White’s children, meanwhile, could have their own reasons for being involved in the crime. Her 24-year-old daughter, Fiona, an economics professor with a history of emotional problems, had a fraught relationship with O’Toole. White’s son, Mark, meanwhile, describes himself as a “tall, dark, handsome 29-year-old lawyer, with a bit of a substance-abuse problem, looking for love and money in what are apparently all the wrong places.” Whether or not one of those wrong places was O’Toole’s condominium is a possibility. It is to LaPlante’s great credit that she keeps so many scenarios active until the book’s final pages.

Set alongside this adroitly handled murder mystery is a second narrative, one that proves every bit as compelling as the whodunit. It involves a different sort of assault, this one on the surgeon’s once formidable brain. In Jennifer White, LaPlante has created an unforgettable portrait of the process of forgetting. Although she functioned as a renowned surgeon just a few years before the novel’s events, she now exists in a “half state,” leading a “life in the shadows.” She needs assistance from a full-time caregiver to perform even the most basic tasks. She is liable to suddenly undress in public and sometimes doesn't recognize her children. Her disease is so wide-ranging that it includes symptoms like prosopagnosia, the “inability to distinguish one face from another.” Not only does her mind wander; so does her body. One epic journey sends her out among Chicago’s homeless, eventually landing her at a free clinic where she once worked.

What makes White’s descent into the void all the more terrifying is that it’s punctuated by moments of startling clarity. While at her old clinic, she is able to treat a patient successfully before being found out. She not only grasps what’s happening to her, but fears that one of her lucid spells might offer up a terrible truth about her friend’s fate. That prospect makes her “beg for exactly that thing I’ve been battling all these long months: sweet oblivion.”

All the while, White’s ability to manage her emotions becomes just as compromised as her cognitive powers. Once known for her steely, aloof personality, she falls prey to all manner of emotional eruptions, some of them shockingly primal. “Ask a dementia patient who she loves, and she draws a blank,” she says. “Ask her who she hates, and the memories come flooding in.” This volatility becomes another item in the growing register of evidence against her. Not that it will matter; she’s already beyond the law. In the end, the suspense of this unique book comes not so much from seeing if the prime suspect is guilty, but rather from finding out if she’ll learn the truth about herself before her mind slips forever away.

Amidon’s most recent novel is ”Security.”


By Alice LaPlante

Atlantic Monthly. 320 pp. $24