THE STRANGE CASE OF JANE O., by Karen Thompson Walker

The man who mistook his wife for a hat; the girl so woefully abused that she developed more than a dozen distinct personalities: Psychiatry’s famous case studies can sound as fantastical as fiction. (And they sometimes were, in fact, too outrageous to be true.)

The 38-year-old librarian at the center of Karen Thompson Walker’s quiet, cool-toned new mystery, “The Strange Case of Jane O.,” though, presents herself as almost pathologically normal, the walking embodiment of a Saltine cracker (hold the salt). Pale, slim and as carefully plain as her name, the soft-spoken Jane gives no reason for her visit when she arrives at the Manhattan office of an analyst named Henry Byrd, and seems to regret it almost immediately; less than 15 minutes after the session starts, she walks out.

Cue the inevitable strange: Three days later, Dr. Byrd receives a call saying that a woman who matches Jane’s description has been found unconscious in a field in Brooklyn’s Prospect Park, without her wallet or phone or ID. The last thing she remembers is dropping her infant son off at day care and walking the four blocks home to make a cup of tea, 25 hours previously.

That’s all catnip to Dr. Byrd, whose preoccupation with his new patient quickly exceeds professional bounds — and only grows when she finally begins to talk. (If not exactly textbook-ethical, his interest is at least not adulterous: Jane is firmly and perhaps congenitally single, and baby Caleb is the product of a sperm donor; Byrd himself is a widower with his own small daughter.)

The case file thickens when she confesses that her problem, generally, is too much memory — her recall of past events, no matter how mundane, is photographic; she’s like a data processor whose human software does not degrade. Then there’s her account of what might have been the inciting incident to her park episode: a run-in on the street with an old acquaintance named Nico Lombardi, who she knows has been deceased for 20 years.

That first reveal, Jane’s remarkable recall, is a rare but real-enough phenomenon called hyperthymesia; the actress Marilu Henner, of the 1970s sitcom “Taxi,” is one of its better-known cases. The second, the inexplicable encounter, lands more in line with Walker’s particular mode of storytelling, a style you might call soft sci-fi.

The author’s widely lauded 2012 debut, “The Age of Miracles,” imagined an Earth whose daily rotation abruptly slows, with a host of unsettling consequences. Her 2019 follow-up, “The Dreamers,” depicted the spread of a baffling, sometimes fatal sleeping sickness on a small college campus a year before the real-world arrival of the coronavirus.

Both of those books were set in Walker’s native Southern California, and concerned themselves less with the mechanical details of their respective dystopias than with the intimate, small-scale dramas of their mostly young and female protagonists. (Doesn’t coming of age always feel like a little bit of an Armageddon, anyway?) What they lacked in plot propulsion or writerly panache was made up for with a kind of gentle, unhurried melancholy, a nimbus cloud of vibes.

Many of the same themes flutter around the edges of “The Strange Case of Jane O.,” particularly in the flashbacks to Jane’s first meetings with Nico. Their tentative connection was the closest she came to making a friend in a high school summer program in Manhattan two decades previously, and those scenes vibrate with the high-key hopes and anxieties of adolescence, the inherent loneliness of being a person in the world.

Walker’s world-building around the opaque adult Jane, though, is less assured. The pages here come larded with Wikipedia bits on psychiatry and semantics (“Webster’s dictionary lists two definitions for the word ache…”) and next to her heady, eucalyptus-scented California, the New York of the novel feels like a borrowed template, a dutiful screen saver in which the “collective, boundless verve” of city life is frequently noted but rarely intrudes.

And while Henry and Jane have every reason to be serious and even somber people, as protagonists they are often, alas, wet blankets. “I’ve been told I can be tedious,” Jane notes at one point, without apparent irony. Pizazz is not a narrative prerequisite, but a little levity and specificity, a more colorful interior world, might have gone a long way toward deeper investment in the characters and their outcomes.

As it is, the story, with its slow-churn revelations and a conclusion that tips toward the supernatural, builds an eerie, incomplete mood: a scrim of subdued intrigue, obscuring stranger things.

THE STRANGE CASE OF JANE O. | By Karen Thompson Walker | Random House | 275 pp. | $28