An intricate puzzle, a powerful setting, and a police detective who is more than a thinking machine. That, plus air conditioning, is the perfect recipe for a summer day.

In SALT LANE, the English writer William Shaw’s latest, Detective Sergeant Alexandra Cupidi --- whom he introduced in THE BIRDWATCHER, his previous novel --- has just moved from London to the bleak-but-beautiful landscape of coastal Kent. After an ill-fated affair with a married colleague, she’s trying to start fresh, and right off the bat she is confronted by two unidentified bodies. She must solve these murders with a squad of gossipy, truculent local police, and she’s working in territory she doesn’t know.

That territory is wild and haunting and precarious, with more birds than human beings. Dungeness, where Cupidi and her daughter live, is itself something of a mystery. In the Middle Ages there was a large town on the site, “but the waves had sucked it away some time in the thirteenth century.… This was a shifting land, built by the sea and then washed away again.” The people in this part of Kent are in constant battle with the water. Every year, according to a local expert, the land has to be reclaimed --- drained and dug out --- otherwise, it would go back to marsh, or to the sea. There is a lonely beauty to the place that Cupidi loves: “In the light of a summer evening, there was something lunar about Dungeness. It lay on the tip of a vast, flat stony landscape that jutted into the Straits of Dover; banks of shingle built over centuries by the churn of tides.” She feels free and alive, “living here on the edge of the world.” London, in contrast, “was exhausted, burning itself out.”

"...a superior thriller... Shaw evokes the treacherous, alluring Kentish landscape with great skill and passion, and the grudging affection between the two coppers makes them an engaging team."

And yet, Cupidi is not really at home here; she’s always been a loner and a misfit, even in London. To start, she’s very tall, 5’11”, and she’s never been great at following orders. She’s frustrated by Zoë, her rebellious, bird-obsessed, purple-haired teenage daughter, and almost equally aggravated by Helen, the prickly, independent mother who, as she sees it, deserted her and her father when Cupidi was a girl. It doesn’t help that Helen and Zoë get along like a house afire.

Zoë also gets along with Cupidi’s third sparring partner: Constable Jill Ferriter, her junior officer (pretty, perky, blond). I loved the byplay between them. Cupidi is more educated, upper-class, experienced and uptight, whereas Ferriter is slangy, cute and flirtatious. In their very first scene --- in the ladies’ room --- Ferriter suggests, none too tactfully, that Cupidi’s appearance needs work before a televised appeal to identify a murder victim. The description of Ferriter’s apartment (artificial flowers, teddy bear, beaded lamp, gold-painted pine cones) says it all about the taste (and class) gap between them.

Gradually, though, they develop a tentative rapport, and Ferriter proves to be brave, compassionate and pretty damned smart; she knows things about the area that newcomer Cupidi couldn’t. But although Cupidi goes so far as to accept a hug from her junior in an emotional moment, Shaw doesn’t turn this no-nonsense detective into a touchy-feely person. “‘When I was assigned to you, I thought you didn’t like me,’” says Ferriter in the aftermath of a dangerous fire in which she’s been injured. “‘Who says I do?’’’ Cupidi replies, unsmiling.

Less successful than the setting or the characters is the complicated plot of SALT LANE. Shaw gives us two threads that initially don’t seem connected. A female corpse found floating in a ditch may be the lost mother of a yuppie-ish Londoner, Julian, who was adopted by an aunt and uncle at the age of two. A male body --- apparently homeless, Muslim, and tortured before death --- is discovered on a local farm that uses immigrant labor. As Cupidi investigates this double conundrum, the reader learns quite a bit of heartbreaking detail about the plight of illegal workers in the U.K. and the history of alternative movements of the 1980s: the women’s protest camp against nuclear weapons at the air base Greenham Common; and the peace convoy, a nomadic tribe of druggy New Age folks who lived in caravans (what we’d call mobile homes). There are also two subplots that, in my opinion, the book could have done without: one involving Cupidi’s ex-lover, now a police superintendent in London, and the other her likable boss, who is in trouble with the British equivalent of Internal Affairs.

I guessed whodunit about two thirds through, but that wouldn’t have mattered if the cadence of the last few chapters hadn’t seemed different from the rest of the book: packed with action, then crammed with lengthy explanations. Every dangling end is accounted for, each ambiguous relationship resolved. I wish Shaw had left things just a bit more open-ended.

Still, this is a superior thriller, as was THE BIRDWATCHER. Shaw evokes the treacherous, alluring Kentish landscape with great skill and passion, and the grudging affection between the two coppers makes them an engaging team. Interestingly, he always refers to Cupidi and Ferriter by their last names, as if intent on giving his female characters a certain professional dignity. I liked that, and I liked them. More, please.