Ruta Sepetys, international best-selling author of 'Between Shades of Gray" and "Salt to the Sea." (Rachel Orr/The Washington Post)

“If you have secrets, I’m your girl.” And it’s true. Author Ruta Sepetys has made a career of researching lost histories and writing them into internationally best-selling young adult fiction.

Her latest book, “Salt to the Sea,” brings to life the largest maritime disaster in history. In 1945, the Wilhelm Gustloff set sail in the Baltic Sea, carrying refugees from World War II. When it sank, more than 9,000 people drowned.

“It’s a story that’s slipped through the cracks,” Sepetys said during a video chat with The Washington Post. Her retelling comes from the perspective of four young adults from different sides of the war: a young Lithuanian nurse, a Polish refugee, a German deserter and a Nazi youth reject.

In many ways, “Salt to the Sea” is a follow-up to her best-known book, “Between Shades of Gray,” which follows a Lithuanian family as they’re shipped off to Siberian death camps by the Soviet Union.

“I write the books, but they’re not my stories,” Sepetys said. “The fact that it’s a bestseller means someone out there is saying, ‘The world has not forgotten you and you matter and we feel for you.’ ”

Sepetys spoke with The Post about Lithuanian feminism, writing a banned book in third grade and feeling ethnic.

This interview is part of “It’s Lit,” a digital Q & A series about women who write books. It has been edited for length and clarity.

Q: You did three years of research for “Salt to the Sea.” How do you condense a complicated period of history into a book that is fun and easy to consume?

A: I do that by focusing on the testimonies themselves. In my first book [“Between Shades of Gray”], when I met with these people who were condemned to these death camps in Siberia, their testimonies were so emotionally charged. [A woman] said, “They took me in my nightgown,” and that ended up being the first line of the book. I rely really heavily on that testimony because it has an emotional authenticity to it.

Q: Is that one of the reasons you’ve chosen female protagonists? That emotional complexity?

A: It’s definitely one of the reasons. There’s also another reason. In Lithuanian culture, the female archetype and female spirit is very important. During the occupation [of Lithuania], the Soviets killed all of the best and brightest men and it was the women who were left to save the culture, the language, the tradition of the county and so many of them used art and music. It was this female higher self that persevered. I mean, the president of Lithuania is a woman.

Q: Do you ever feel frustrated about how history is taught in the United States?

A: I often wonder what determines how history is preserved and recalled. Why is it that some parts of history become part of our collective consciousness and other parts of history remain hidden? This troubles me. It keeps me up at night.

Q: You wrote your first book in third grade, and you said it was banned. Why?

A: My teacher in third grade said true creativity is taking the expected and making it unexpected. Well, in the ’70s there were these things called After School Specials — it was all about ‘Don’t do drugs’ or stranger danger. So in order to take the expected and make it unexpected, [main character] Betsy’s adventures were with a 35-year-old dude who lives in a van. I thought it was super-creative. And one of my friends took it home, and her mom read it and just, like, freaked out about the stranger danger and that I was saying it was okay to go with a man in a van.

Q: What was it like to grow up in the Midwest with a name like yours and such an unknown culture?

A: It had a profound effect on me to the point where I believe that even writing my first book, it was probably just a search for my own identity. Growing up in Detroit with this name, I felt pretty alone. I didn’t really learn the history of [Lithuania] until I was in my teen years, so it did have an impact on me. A sociologist I met asked if I felt ethnic, and I definitely did. So, reading books not only makes you less lonely but writing makes you less lonely. Every day, I am meeting people that I always think, “Man, where were you when I was a kid?” I felt so weird and like such an outcast, and yet so many people shared my same path.

Everdeen Mason is an audience editor at The Washington Post and Book World contributor. You can follow her on Twitter: @EvMason.

Read more from “It’s Lit”:

How racism and prejudice inspired Sabaa Tahir to become an author

V.E. Schwab has had enough of the ‘classic female’ role in fantasy

How Marie Lu found out that fantasy books didn’t have to have white heroes