Enough with the complaints, Metro riders — things could be a lot worse!

In ex-cop Clare Mackintosh’s smashing second novel, “I See You ,” unsuspecting women using the London subway system are targeted by a madman.

In the novel’s first sentence, commuter Zoe Walker tells us “The man behind me is standing close enough to moisten the skin on my neck with his breath.” That’s creepy enough, but the dangers will multiply for Zoe and other women who venture into a “cramped, malodorous train,” far beneath the city.

"I See You," by Clare Mackintosh (Berkley)

Zoe already has trouble enough aboveground. She’s 40 and divorced, with a son who’s 22 and daughter who’s 19. Her kids don’t like her new boyfriend, nor does either of them show much interest in finding work or leaving home. Then, on the train one day, commuting to the job she hates, Zoe is shocked to see her photograph in a newspaper advertisement for some kind of dating service. There’s a phone number, but when she calls, no one answers .

“I’m worried for me,” Zoe confesses. “I don’t know what these adverts mean, or why my photograph appears in one, but the danger is very real. I can’t see it, but I can feel it. And it’s getting closer.”

In time the danger becomes very clear, thanks to another admirable woman, police officer Kelly Swift, who patrols the subways for pickpockets and other wrongdoers. It’s a lousy assignment, but she’s on probation because she attacked a prisoner, a rapist who wised off at her. Kelly’s twin sister was raped in college, and she has no sympathy for predators.

Kelly and her partners learn that men pay big money to access a mysterious website that gives them information on scores of women who ride the subway: a picture, along with the woman’s age, home address, place of employment and the details of her commute. The site also notes how “difficult” a woman is, from “Moderate” to “Extremely Challenging.”

The site is a stalker’s dream come true. After police learn that at least two women listed have been raped and murdered, they are desperate to learn its origin and ownership.

We readers sometimes hear from the unknown person behind the site, who sends out brief, mocking, anonymous comments like:

You could call me a broker; a go-between; a matchmaker.

And the beautiful thing is that none of you even know you’re on my books.

Who is this sinister manipulator? Is he (or she) someone we’ve met? Zoe’s ex-husband, who still yearns for her? Her erratic new boyfriend? Her obnoxious boss? The nice couple next door? The older man who’s dating her gorgeous daughter? When the daughter is abruptly listed on the site — with an “Extremely Challenging” rating — Zoe is terrified. So are we. Horrors ensue.

The author Clare Mackintosh ( Charlie Hopkinson )

Mackintosh spent 12 years as a police detective in rural England, then resigned in 2011 to focus on raising her three children. She also set out to write a novel. Her first thriller, “I Let You Go,” published in the United States last year, tells of another woman in danger: She faces prison for something she didn’t do. The book received richly deserved praise and was an international success.

Mackintosh understands the complexities — the endless ups and downs — of police work and family life, and she presents them with skill and sensitivity. Beyond that, her greatest gift may be her plotting. About halfway through “I Let You Go,” she introduced a shocking twist that turned her tale on its ear and carried it to a new level. Now, in “I See You,” she hits us with an equal astonishment at her story’s very end. She’s a master of surprises.

Perhaps because of Mackintosh’s years of police work, her first two novels reflect an exceptional sense of evil; they feature three characters who, despite their charming exteriors, are pure psychopaths, creatures who would cut your throat for a dime. She offers good people, too, but it’s her recognition of inhumanity that has made her books brilliant and unnerving. It’s hard to choose between her novels. Read them both. What matters is that Mackintosh seems destined to do important work for many years to come.

Patrick Anderson regularly reviews mysteries and thrillers for The Washington Post.

i see you

By Clare Mackintosh

Berkley. 372 pp. $26