Cara Black lives in a modest house in Noe Valley, but in her mind she spends her days in Paris: combing the garment district in the Sentier, sniffing out clues in the sewers beneath the River Seine, exploring the inner courtyards of the exclusive Ile Saint-Louis.

In Black's imagination, she leaves San Francisco and becomes Aimée Leduc, the detective heroine in a series of best-selling murder mysteries. Tall, thin and waifish, Leduc runs her own detective agency on the Right Bank of Paris. "Murder on the Ile Saint-Louis," the seventh in Black's Leduc novels, last week reached the No. 2 spot on The Chronicle's Bay Area fiction best-seller list.

"I'm not French," says Black, a former preschool teacher who never wrote a novel until she was in her 40s, "but I'd gone to a French Catholic school in Menlo Park where we learned this archaic French from the nuns. My dad was a Francophile and my uncle went to France after World War II on the GI Bill to study art."

Each of the Leduc novels takes place in a different arrondissement of Paris. The idea came to her during one of her frequent visits to Paris, when she was waiting for a bus on the rue du Louvre and saw a vintage neon sign saying "Duluc Detective." She went inside and introduced herself to Madame Duluc, the owner of the agency.

"I thought, I can't write like a Frenchwoman," Black says. "I can't even tie my scarf the right way. But maybe Aimée could be half French and half American."

In some ways, the Leduc series is wish fulfillment for Black. "She's thinner, taller (than me). I always have her do things I'm scared to do. Climb ropes -- I'm afraid of heights. I have her deal with rodents -- I'm afraid of mice and rats. She does things on the computer I can't."

Whereas Black is conservative in appearance, Aimée is quirky, wears her hair in an androgynous spiky 'do and is too busy for manicures and other refinements. Often overwhelmed by work, she tends to do things like leave her trusty Beretta in the spoon drawer. She lives in a 17th century townhouse apartment with her Bichon Frise, Miles Davis (pronounced "Meals Dah-VEECE"), and works with her dwarf male partner, René Friant.

Unlike Aimée, who is attracted to bad boys and a serial loser in love, Black has been with the same man for 31 years. Her husband, Jun Ishimuro, owns and operates Foto-Grafix, a photography bookshop in the Cartoon Art Museum on Mission Street near Third Street. Their son, Tate, 17, is a senior at Stuart Hall High School.

Black, who doesn't give her age, is wearing a black cashmere sweater, capri pants and metallic, ballet-like flats from Paris. She's soft-spoken, modest in affect and looks a tad like Joan Didion did 15, maybe 20 years ago. She previously worked at the Jewish Community Center preschool and later was director of the Stonestown YMCA preschool. She laughs when asked if she ever expected to be the author of a popular detective-novel series.

"No! I'm just a mom, right? I was a preschool teacher. I was hanging out in the Noe Valley playground with my kid in the sandbox."

The Leduc series started in 1999 with "Murder in the Marais," into which Black wove the story of a friend's mother: a woman who, as a Jewish teenager in 1943, had come home to an empty apartment. Several years later, she learned that her parents and sister had been taken to Auschwitz and executed by the Nazis.

"I never intended to write a series," Black says. "I just wanted to write a story about my friend's mother." When she went to a mystery conference at Book Passage in Corte Madera, and later when she visited Paris, the story began to take shape.

"I knew I needed a detective, and I had this familiarity with French. So I thought, 'Well, I'm going to interview some detectives.' " She found three Parisian women who owned their own agencies, each very different from the others. Her favorite was Madeleine Dieudonné.

"She's in her mid-60s. She's short, stocky. Kind of like a fireplug. An older grandma type. We were talking and she said, 'I'm sorry, I have to go. I have to go do surveillance.' I said, 'You do?' It was really cold outside. 'Where do you do it?' She said, 'My car.'

"I said, 'Don't they recognize you after a week if you're there every day hanging around this street near the Gare du Nord?' She said, 'Look at me. Don't I blend in? Do you think anyone suspects me?' I thought, 'That's so cool. She's really sharp.' "

Like any novelist would do, Black pumped Dieudonné for information, and then did the same with Dieudonné's apprentice, a young Cambodian woman named Kim who buzzes around Paris on her motorbike and keeps a wardrobe of disguises in the trunk of her car.

All of that was fodder for the Leduc "investigations," as Black calls her novels. The rest of the research is done on foot. She goes to Paris twice a year usually, spends a couple weeks at a time ("I have a kid; I can't stay for long") and crashes on the couch of friend who lives in Montmartre.

Once she settles in, Black says, "I go into sponge mode. I just find a place. There has to be something that really speaks to me and I think, 'Could crime happen here? What kind of crime? Who lives here?'

"I listen. I read the paper. I have a friend who's a policewoman and I'll take her out to lunch and say, 'What do you think? Could this kind of crime happen here?' and she'll go, 'No no no. That isn't the kind of thing that occurs here, but this does."

Black's books have built slowly and started selling in significant numbers with the fourth title, "Murder in the Bastille."

"I think I have two audiences," she says. "There are mystery readers, and then Francophiles who want to read about France. I get a lot of people who'll say, 'I don't normally read mysteries but I love Paris.' "

"Cara Black books are good companions," wrote critic and fellow mystery writer Alan Furst. "Fine characters, good suspense, but, best of all they are transcendentally, seductively, irresistibly French."

Right now is a good time to be a mystery writer, notes Black, who is president of the Northern California chapter of Mystery Writers of America and makes frequent appearances at Bay Area independent bookstores. "I mean, look on the New York Times best-seller list. There's a bunch of mysteries."

The genre has evolved, she says, from the circumscribed, "locked-room mysteries" of Agatha Christie. "They're more than just 'whodunits.' There's social and political comment in these mysteries. Often the detective is flawed or the story is set in a different segment of society than we would ordinarily visit and the writer gets to explore those issues."

Black spends a year to a year and a half on each novel -- including writing, research and travel to Paris. "If you have a series and the publisher likes it, they want you to keep doing one a year." She loves the work, and says the specific parameters of the mystery genre are an advantage to the writer.

"You've got the crime, the inciting incident -- whether it's murder or robbery. There's an investigation; things get worse and they spiral. There are clues, red herrings. And there's a climax: things comes to a head and there's a resolution."

It's that factor, Black believes, particularly in a world that gets more fractious by the day, that explains the growing popularity of thrillers and detective fiction. "We get a resolution. Some form of justice is served."