The opening of Leo Tolstoy’s “Anna Karenina” is one of the most familiar lines in all of literature—“Happy families are all alike; every unhappy family is unhappy in its own way.” It is widely recognized for its universality, hinting at the private problems every family conceals.

Author Sande Boritz Berger is no exception, and in her debut novel, “The Sweetness,” she explores the origins of her own family’s unhappiness, hidden from her for so long.

“As a child, I could see that there were a lot of secrets and lies in my family—a lot of depression,” she said last week during an interview at her home in Bridgehampton. “I felt there was so much more I didn’t know. I guess that void was enough to create a certain sensitivity in me that eventually led me to want to unravel the truth.”

The result is a “fictionalized family history,” according to Ms. Berger, set in 1941, deep into World War II. The story revolves around the lives of two young girls from separate branches of a Jewish family from Lithuania. Mira lives in Brooklyn with her immigrant parents, dreaming of running off to Hollywood. She has everything compared to Rosha, her cousin, who still lives in Lithuania and struggles for her very survival against the invading Nazis.

Ms. Berger’s portrayal of the two young heroines harks back to her childhood passion for writing. Splitting her time between Manhattan and the East End, she worked for nearly two decades as a scriptwriter and producer before returning to her first love. She graduated from Stony Brook Southampton’s MFA Program in Creative Writing and Literature in 2009, where she studied different writing techniques from authors, including Frank McCourt, Meg Wolitzer, Roger Rosenblatt, Matthew Klam, Melissa Bank and Lou Ann Walker.

“I was writing a novel about my maternal grandparents who lived in Brooklyn when my aunt, who was 99 at the time, showed me an old photo a young girl,” she said. “My aunt wouldn’t talk about her and no one in my family knew what happened to her.”

She found the girl’s birth certificate and, on a hunch, researched her history through Yad Vashem, the authority on Holocaust research. Ms. Berger discovered that the girl—her second cousin—was from Vilna, Lithuania, and lived in one of the first Jewish ghettos rounded up in the Nazi invasion.

“I was taking a class with Lou Ann Walker in the MFA Program and started writing a story about the girl in the photo,” Ms. Berger said. “From there, it developed organically. I didn’t sit down one day and say, ‘Today I am going to write a book.’ I wrote complete short stories and liked my characters enough to keep going with them, using each story as a chapter.”

Published by She Writes Press, “The Sweetness”—which officially hits shelves on Tuesday, September 23—was a semi-finalist in Amazon’s yearly Breakthrough Novel Awards and has already sold 1,800 copies online to mixed reviews. “One girl wrote me a letter that said the book made her want to be a better person,” Ms. Berger said, while another “described it as ‘Holocaust Lite.’ I laughed about it, but I don’t think my grandparents would have.

“I wrote this book for my family, for my children and my grandchildren,” she continued. “I don’t expect to make any money, I just hope it has a good run for a few months, and then I want to go back to writing.”

For more information about Sande Boritz Berger, visit sandeboritzberger.com.