Like the main characters in her new novel “Shadow Child,” the estranged twin sisters Hana and Kei, author Rahna Reiko Rizzuto grew up on the Big Island and is of Japanese-Caucasian descent. Race, identity and forgiveness are central themes in this psychological mystery set in Hawaii in the 1950s and ’60s, New York City in the ’70s and California and Japan during World War II.

Rizzuto, 54, graduated from Hawai‘i Preparatory Academy and Columbia University, where she was the first woman to receive a bachelor of science degree in astrophysics. Her first novel, “Why She Left Us,” won an American Book Award in 2000; her memoir, “Hiroshima in the Morning,” was a finalist for the 2010 National Book Critics Circle Award.

The author spoke with the Honolulu Star-Advertiser by phone from her home in Brooklyn, N.Y., following the May release of “Shadow Child” (Grand Central, $26).

QUESTION: In “Shadow Child,” Hana says her eyes — one dark, one light — “just screamed hapa haole in our little Hawaiian town,” where she and Kei “were two of the few privileged and damned creatures of mixed race.” What was your own experience like?

ANSWER: My mother, Shirley Rizzuto, was Japanese-­American from Hawaii and my father, Jim Rizzuto, was Italian from New Jersey. I was born on Oahu and my mom’s family — her maiden name is Ozaki — is all still there. All my mothers’ brothers and sisters married non-Japanese, so all my cousins are hapa.

I was raised in Waimea on the Big Island. My parents worked at HPA: My dad taught calculus and was head of the math department, and my mother was a college counselor and director of publications.

I had a lot of local friends, day students flowing in and out of this kind of slightly more haole structured community. I remember parents of local friends talking about having to speak standard English at school and be a different person.

It was a little like being in two worlds.

Q: Where did Hana and her twin grow up?

A: I set the book in an unnamed town, but it’s based on Hilo. I didn’t name it because there are not a lot of stories about Hilo and I didn’t want people to pick up the book and think they were reading the one Hilo story. There’s a billion stories (set) in New York, so nobody’s going to think that any one story defines New York.

Hilo in the 1960s is different from now. The people are different. The pidgin is different. I was hoping that people would want to know more about it, read more Hawaii authors.

Q: How did you happen to major in astrophysics in college?

A: One summer during college, I had a job with the Canada-France-Hawaii Telescope Corp. I was up on Mauna Kea, taking pictures of globular clusters, and I got really interested in astronomy and astrophysics.

Q: From there, how did you become a writer?

A: Writing and reading were always part of life in our house. My dad wrote a fishing column in West Hawaii Today; Mom was a columnist for Hawaii Fishing News, editor of Hawaii Tennis News and author of the “From the Fishwife” cookbook series.

After college, I worked for Knopf in their publicity department and got to travel all over with their authors. I spent a lot of time with writers like Toni Morrison and Vidia (V.S.) Naipaul, but thought I could never write because they’re so good.

Then, when I was about 30, my mother discovered that she was born in L.A. and she and her whole family had been in internment camps during the war. When they got out of the camps they went to Hawaii, where my grandfather was from.

I thought, there’s a story here I didn’t know and wanted to know. That started me writing because I felt I finally had something I needed to say. My first novel, “Why She Left Us,” tells the story of a family that was interned in a camp.

Q: How did you come to write your memoir “Hiroshima in the Morning”?

A: I had a great-aunt who had been interned in Jerome Camp. When she was released, she went to Japan to work for the American occupation, with a group of doctors in Hiroshima and Nagasaki, measuring and trying to study the effects of the atomic bomb on humans. She became a raging peace activist in Berkeley for the rest of her life.

When writing fiction, you need to get the little details, the sensory stuff. I went to Hiroshima to research the character of Lillie (the twins’ mother) in “Shadow Child” on a grant giving funding for six months in Japan.

I arrived in 2001, three months before 9/11. I didn’t read or speak much Japanese and I was there alone, working through a translator. A lot of people had become kind of professional storytellers, telling the same story over and over. Others wouldn’t talk to me.

On Sept. 11, my mother and father were visiting New York, helping take care of my kids. My husband was on the Brooklyn Bridge, saw the plane, called my parents and said, “Go get the kids,” who were in preschool and kindergarten.

In Hiroshima, people around me who experienced the original ground zero were seeing this new ground zero, and suddenly all the stories I wanted to get were coming out of them. It had unblocked their memories. People were calling, inviting me to come for a second interview or a first, if they’d been avoiding me.

I decided to put the novel aside and write a memoir about the stories they told me.

Q: Now the novel’s published, and the Hawaii sections read as if you’ve returned a lot.

A: Yes. My ex-husband also grew up on the Big Island, and we brought our sons, Kalei Tooman and Kai Rizzuto, two or three times a year, starting when they were 3 months old. They are now 22 and 20. And my partner now, I met in New York and found out his family was living in Waikoloa. I think that’s one of the reasons why we clicked.

Q: The twins are older than you. How did you re-create their Hilo, including the 1960 tsunami?

A: I did a bunch of interviews about what it was like to grow up in Hilo at the time, and how the twins might have been treated. I hung out at the (Pacific) Tsunami Museum talking to docents, reading oral histories. I talked with Walter Dudley, author of “Tsunami!”

Q: What do you miss from the Big Island of your childhood?

A: (Some) things I miss are no longer there: Hayashi Store, The Deli, the cowboys riding along the side of the road, the old post office with hitching post, no traffic light in town, driving over the lava from the upper road to Kona in a four-wheel drive to go camping at the beach, the Old Hawaii on Horseback parade, all of Hapuna Beach. The fishponds at Kapoho where we used to swim on summer vacations; the community plays we used to put on where Parker School now is. Knowing everyone, or their brother, cousin, sister’s best friend. Fishing with my father.

Things that are still there that I love: Hiking up to Buster Brown and the White Road hike into the back of Waipio, snow on Mauna Kea, (the remaining) half of Hapuna Beach, Two Step (snorkeling spot), the turtles at Kiholo Bay, the rodeos, the volcano erupting, Hawaiian music, Spam musubi and malasadas, plate lunch at the beach, shave ice, the Kaumana Cave. The ocean.

Q: When were you last there?

A: I spent about half of last year there trying to settle my dad’s estate. My mom passed away in 2010.

My dad left my younger son his boat and all his fishing equipment. Kai spent a summer working on one of the charter boats in Kona when he was 15, and at 16 he caught a grander, a 1,000-pound marlin. The fishing community in Kona, he’s one of their own.

Q: What do you miss most?

A: Something about the smell of the ocean, all the Hawaiian smells, the air is different, so every time I get back I think, why do I ever leave?