“Moonlight Mile” is the sixth of Dennis Lehane’s Kenzie-Gennaro books, the first in 11 years and the first since “Gone, Baby, Gone,” with Casey Affleck as Patrick Kenzie and Michelle Monaghan as Angie Gennaro, came out in theaters in 2007.

For fans of the Boston-based detective couple — a blue-collar Nick and Nora Charles, putting their relationship to the test in the face of thugs and bums, ethical dilemmas and a balance-challenged checking account — the return is more than welcome. And for new initiates, “Moonlight Mile” is as good a place as any to begin, even though it’s a sequel of sorts.

It’s been 12 years since Amanda McCready, the sorry little sprout of “Gone, Baby, Gone,” went missing. The dangerous, twisting path that Kenzie and Gennaro took to find the 4-year-old feels like ancient history to the couple. But one brittle, late-fall day, Kenzie sees a vaguely familiar face waiting for him: Beatrice McCready, Amanda’s aunt from all those years back.

Her niece, a teenager now, is missing again.

But things are different for Kenzie and Gennaro these days: They have their own young daughter. He’s been working for a high-end investigations firm and is close to getting a full-time gig there; Gennaro’s taking care of the kid and studying for a master’s degree. They’re broke, and the Great Recession is evident everywhere around them.

(“Moonlight Mile” can be read as a primer for couples struggling to make it through these economic hard times with their emotional lives, and their marriage, intact.)

So does Kenzie take the case? Of course. And does Gennaro get sucked into the ensuing whirlpool of crackheads, identity thieves, Russian mobsters, and weird fitness gurus? Roger that.

The plot of “Moonlight Mile” is mapped out with Dashiell Hammett-like precision, but as with Hammett, when Lehane’s on his game, it isn’t the plot that matters. It’s the characters, and the smart, hard-boiled prose.

Here’s Lehane — well, Kenzie, the first-person narrator — on the dynamics of the spousal relationship, after he’s just come home from being abducted, assaulted and threatened:

“She frowned and I could feel both of us trapped inside ourselves, not sure what to do with today’s violence. There was a time we would have been experts at it. She would have tossed me an ice pack on her way to the gym, expected me to be raring to get back to work by the time she got back. Those days were long gone, though, and today’s return to easy bloodshed drove us into our protective shells. Her shell is made of quiet fury and wary disconnection. Mine is made of humor and sarcasm. Together we resemble a comedian failing an anger-management class.”

Not everything works in “Moonlight Mile.” Lehane struggles to get the voices of a bunch of privileged prep-school girls right — Amanda, exceptionally smart and solitary, had engineered her admittance to an elite girls school on a full scholarship before she disappeared.

But Lehane knows Kenzie and Gennaro inside and out, and here they are, older but not necessarily wiser — although still cracking wise — a full decade on, worrying about the bills and middle age and parenting. And worrying about threats of death and bodily harm and getting shot at by crazed criminals.