Published almost simultaneously, these mysteries from London form an interesting pair. Each features a troubled Englishwoman who takes an almost morbid interest in another person or persons. At first merely voyeurs, the two women soon become meddlers.

The “girl” of Paula Hawkins’s “The Girl on the Train” is Rachel: divorced, an alcoholic and a commuter into London. Her train makes a regular stop alongside a row of houses, one of which she used to live in with her husband. He still lives there with his second wife, Anna. But Rachel is even more captivated by another house a few doors down. Repeatedly, she catches glimpses of the glamorous young couple who live there. Their mutual tenderness inspires Rachel to make up names and occupations for them and to idealize their relationship — a fantasy that may help compensate for her own lost marriage.

One day, however, Rachel sees something jarring from the train: the glamorous wife, Megan (her real name, as Rachel will soon learn), in a compromising situation with a man who is not her husband. Rachel’s life is bereft of meaning — she has no job (the commuting is a sham), and she sometimes gets so drunk she can’t remember what she did under the influence — and the sight energizes her. “It’s been a long time since I’ve had anything worth keeping a clear head for,” she admits while wondering what to do about the transgression she witnessed.

Soon, the adulterous Megan disappears. Rachel is now faced with a daunting to-do list: stay sober; placate Anna, who detests Rachel (Anna’s husband continues to see Rachel and occasionally gives her money when she runs out — never mind that she’s almost certain to squander it on drink); and help Megan’s cuckolded husband search for her.

“The Girl on the Train,” Hawkins’s first thriller, is well-written and ingeniously constructed — perhaps a bit too ingeniously. The first-person narrator is now Rachel, now Anna, now Megan, and some of Megan’s soliloquies date from long before her disappearance — yet are strategically inserted between present-day chapters related by Rachel and Anna, making the reader feel a bit manipulated. But the portrait of Rachel as a chronic drunk who just might save herself by playing detective is rich and memorable.

“Her” by Harriet Lane. (Little, Brown)

What the reader is supposed to make of Nina, the 40ish watcher of Harriet Lane’s brilliant “Her,” takes longer to become clear. As the novel opens, she spots someone whom she believes she knew long ago: Emma, who is about 15 years younger. By the end of the first chapter, Nina has made up her mind: definitely Emma. Over the next few months, Nina slowly and craftily cultivates Emma, even playing hard to get, as the women give their perspectives on their growing friendship in alternating chapters. (Why Emma doesn’t recall Nina is one of the story’s several mysteries.)

Tension builds as Nina begins to perform secret and senseless cruelties. Although luring Emma’s young son away from his mother is mean, it at least dovetails with Nina’s campaign: She ingratiates herself with Emma by “finding” the boy and returning him unharmed. But does Nina have to hold back the kid’s scooter and make sure he never rides it again? As Nina insinuates herself deeper into Emma’s life, the reader’s anxiety is compounded by the likelihood that all this nastiness is payback for some wrong that Emma did to Nina a long time ago — but what? The story reaches a wrenching climax when Nina manages to lure Emma and her family to Nina’s vacation house in the south of France.

Lane is a fine stylist, especially when describing nature. “Rain hits the window in fits and starts, as if it’s being flung in handfuls. . . . It’s getting dark, the air full of stars and the surging tidal percussion of crickets.” And here is the bravura ending to Nina’s lunch with her father at a fancy restaurant: “We stand on the pavement outside . . . for a few moments, saying our goodbyes, moving aside as people weave in and out of the heavy doors leaving little incomplete jokes hanging in the air behind them like smoke.”

The reader of “Her” has only two first-person narrators to keep track of — Nina and Emma — and the author switches smoothly and naturally from one to the other. As the number of pages left in “Her” dwindles, you may find yourself wondering (as I did) if Lane has given herself enough room to wrap the story up satisfactorily. Trust me, she has.

Drabelle is the mysteries editor of Book World.

THE GIRL ON THE TRAIN

By Paula Hawkins

Riverhead. 323 pp. $26.95

HER

By Harriet Lane

Little, Brown. 261 pp. $26