Memory makes unreliable witnesses of us all, but knowing that usually doesn’t change the way we operate. What are we to trust as we move through the world if not our firsthand perceptions, so intrinsic to the cartography of our lives? If our own recollections are false, if our understanding of pivotal events proves to be misunderstanding, where are we then?

And, by the way, what time is it?

Time slips in and out of an uncertain present shadowed by the distant past in Poppy Adams’s “The Sister” (Alfred A. Knopf, 273 pages, $23.95), a terribly British novel that unfolds over several spring days at Bulburrow Court, a once-grand house on a sprawling estate in England’s West Country. For nearly half a century, its sole inhabitant has been Virginia Stone, a genteel oddball who grew up there with her family and has grown old there alone, so detached from the outside world that she has no telephone.

Tethered to the moment via her bevy of clocks and watches, whose accuracy she checks with some desperation, she has devolved from cosseted misfit into village eccentric, or perhaps something more pitiable; it’s hard to tell, initially. As Virginia is the narrator of the story, we must rely on her comprehension of the events she relates, and in that we are at least as handicapped as she is. Reading human beings, herself included, is not one of her abilities.

“I might have a poor understanding of people, but I have an instinct for insects,” she explains, and it’s true: Moths have been her lifelong obsession, as they were for her lepidopterist father — who was nearly as socially ill-equipped as she is — and for her grandfathers before him.

But as the novel begins, some skill with people would be more helpful. Virginia is anxiously awaiting her lively, mercurial younger sister, Vivien, whose imminent and not altogether welcome arrival is about to put an end to her solitude. It is also about to put an end to the peace Virginia has made with her memories. People in a family, as even she knows, never have the same recollections of the lives they lived alongside each other.

Vivi is leaving London to come home for good, though she has neither been to Bulburrow nor spoken to her sister in 47 years, since shortly after the death of their mother. The reason for Vivi’s return is as mysterious to Virginia as is the cause of her sudden abandonment after two decades of closeness between them.

It was a childhood in perfect balance, so I’m wondering what it was that came along and changed everything. It wasn’t just one thing. There’s rarely a sole cause for the separation of lives. It’s a sequence of events, an inexorable chain reaction where each small link is fundamental, like a snake of upended dominoes.

If there is a voice-over quality to Virginia’s words, it’s to be expected. Ms. Adams is a television documentarian, and her writing has a cinematic feel: Virginia peers out the window, watching for Vivi, and we see the drive winding through the grounds as if a Merchant Ivory production were unfolding before us. Then the camera pulls back to show some Victorian Gothic interior, and we fade to a flashback.

There is also an occasional, saccharine Winnie-the-Pooh quality to Ms. Adams’s writing (“It’s just not what I call the Normal Order of Things,” Virginia frets), as well as a direct-address conceit that is both more pervasive and more problematic. “Did I tell you I’m actually quite a famous lepidopterist?” Virginia asks the reader. Later she burbles, “I have no idea why, and I’m sure you’ll say there were far more appropriate things to think at the time.” There is no apparent reason for this recluse to tell her story to us, or to anyone but herself. Within the world Ms. Adams has created, this device breaks the rules of logic.

Beyond those distractions, however, Ms. Adams spins a suspenseful, provocative, deliberately ambiguous tale about decay and disrepair — of people and the bonds between them — and about the harm that comes from even well-intended secrecy and silence, two pillars of life at Bulburrow Court.

It is also, of course, a story about what happens when a human being is shaken out of a hibernation that has lasted most of her life. Watching a dormant fox moth caterpillar in winter, Virginia marvels:

What was it … that enabled it to adjourn life so effectively, and how is it that something as simple as the warmth of the sun can restore it, can get the tiny valves pumping once again, to shunt along its cold, stagnant blood? … Is this, in fact, a resurrection?

For Virginia, Vivi’s return is the catalyst for her own return to life. Which, as it happens, isn’t necessarily a good thing.