After visiting the Asian Art Museum to see an exhibit on Shanghai years ago, Amy Tan picked up a book in the gift shop about courtesans there in the early 20th century.

"A few days later, while leafing through the pages, I came across a photo of 10 women, which stunned me," Tan writes on her website.

"The caption said: 'The Ten Beauties of Shanghai.' They were courtesans who had won a popularity contest in 1910. Five of the young women are dressed in the same clothes my grandmother is wearing in one of my favorite photographs of her."

This is how Tan learned that her beloved grandmother, the woman she'd long seen as her muse, probably worked in a brothel. It stopped her in her tracks and led her to completely change the course of the novel she'd been working on.

The result is "The Valley of Amazement," set at the dawn of the 20th century, Tan's first novel in eight years.

Like Tan's "The Joy Luck Club," it's the story of a tense relationship between a mother and daughter, and of the clash between East and West.

But this time the central character is forced to work in a Shanghai brothel, so for the first time Tan writes explicitly about sex.

During her 25-city book tour this month, Tan appears at Copperfield's in Petaluma on Dec. 2 and at Book Passage in Corte Madera on Dec. 7. Here are excerpts from an interview with her.

Q: How does your writing help you learn more about yourself?

A: Everything I'm writing about has to do with identity, self-identity. It has to do with the meaning of my life, with who I am and what I'm looking for. The predominant influence would be my mother, and that accounts for why a mother figure appears so often in my books. I cannot seem to get away from it.

Q: Were you concerned about writing about a part of your ancestor's life that some might see as not virtuous?

A: It was difficult -- not simply because of what the family would think. It was hard because my grandmother is my muse and I often feel her in the room with me. By even considering she might have been (a courtesan), I feared I might offend her, especially if it had not been true. And if she had been, I feared that she wouldn't want people to know.

I also feared that mother -- she died in 1999 -- wouldn't want people to know. Yet I think that my mother and grandmother were strong believers in truth and that they'd think it (openness) is a good thing.

I decided to write about courtesans because I could not stop thinking about that world. It is not a story, however, about my grandmother.

Q: Your central character, Violet, is half white and half Asian.

A: You have a girl who thinks she's American and looks down upon the courtesans even though they're like her sisters. Then she's flipped into the other world. And she's become that other half: Chinese.

She's become actually less than that other half. If you're Eurasian (in early 20th-century Shanghai), you don't belong to either world. So she has really taken a tumble, and she has to remake herself. She has to understand and figure out who she is.

Q: Let's talk about sex. "The Valley of Amazement" isn't "50 Shades of Tan," but are you concerned that people might take this book less seriously than your other work?

A: So many of my readers want that mother-daughter story -- and while this is a mother-daughter story, I don't think they would expect the mother to be running a courtesan house and the daughter to be a courtesan. I don't think I've had a sex scene in another book. There are people who do object to the sex in there. Some reader reviews say "Sex -- this is horrible."

Q: Was it difficult to write about sex?

A: I was afraid to write corny love scenes. I was also afraid that people would think they were peering into my bedroom, that this was my sex life, especially if they've seen photos of me dressed as a dominatrix (which Tan once did while playing with the Rock Bottom Remainders, a rock band made up of authors).

Q: You talk about secrets in your family. Can secrets be a gift?

A: I love the secrets. I thought 'I'm done -- I've found out as much as I can about my family -- my mother has died.' But after learning about my grandmother, I'm encouraged by knowing I probably will never be done finding out secrets in the family.

Michael Shapiro writes about entertainment for The Press Democrat. Contact him at michaelshapiro@pressdemocrat.com or visit his site: www.michaelshapiro.net.