When Rudi Raab decided to bring his Jewish girlfriend to meet his parents in Germany 25 years ago, he wrote them a “guess who’s coming to dinner” letter. He had reason to be nervous: His father had been a high-ranking Nazi official in Hitler’s regime.

The reply, Raab recalled, came from his mother: “OK, what can’t she eat?”

Thus, in 1990, Raab brought Julie Freestone to sit down separately with his mother and father (by then divorced), and interview them about their experiences during the Third Reich. Raab, who had always been afraid of his father and his violent temper, had never spoken to him about his wartime experiences.

“I almost fainted when I had to translate her questions and look my father straight in the eye,” said Raab, 70.

When Raab and Freestone started dating in 1989, they were an unlikely couple. Freestone, a freelance reporter (and former correspondent for this publication) was liberal — and brought up by “good Jewish parents” in the Bronx who were suspicious of anything German.

Raab, a Berkeley police officer, was more conservative — and German. The two met when Freestone interviewed him for a story about the war on drugs.

“I was sure that anyone who grew up with a father who was a high-ranking Nazi had to be anti-Semitic,” Freestone, 70, recalled.

Still, Freestone said, she always admired a man in uniform, and thought Raab was smart and good-looking. They began to date casually, though neither was looking for a relationship. Raab was recently divorced, and Freestone, too, had been previously married (both have sons from other relationships).

Their relationship might have fizzled out, Freestone said, had they not unexpectedly been inspired to investigate their families’ pasts.

Freestone wanted to write a story about a two-day reconciliation workshop in Sausalito that brought together the children of Holocaust survivors with Germans born after World War II. The workshop leader, therapist Armand Volkas, wouldn’t let Freestone sit in unless she participated, and she needed to bring Raab to keep the numbers of Germans and Jews even.

“Rudi, believe me, did not want to go,” she recalled.

Freestone herself didn’t quite fit the workshop model: Her parents weren’t Holocaust survivors, but her family had its own postwar story. Freestone’s father, who worked for the U.S. Immigration and Naturalization Service, brought his wife and children to Germany after World War II. He worked for the U.S. government for three years helping relocate Jews. Freestone said it was an isolating and miserable time for her mother.

 “I think the last place on Earth that my mother wanted to be in 1948 was [post] Nazi Germany.”

Raab, who saw himself as a “superhuman” strong cop, was so moved by his experience in the workshop that he wrote a poem about the shared responsibility of the children of the oppressed and the oppressors. “We shall never let the victims be forgotten/ for if we do, we will forget that the perpetrator can be in all of us,” he wrote.

And he and Freestone began researching and writing about their family histories.

That project is now bearing fruit: This year the couple, who live together in Richmond, are self-publishing a novel called “Stumbling Stone,” based on their relationship and family backgrounds.

“I think it’s a romance wrapped around a mystery with major historical connotations,” Freestone said of the lightly fictionalized work. The book, which alters names and certain details, follows the couple’s journey as they peered into their own pasts and homed in on the story of Raab’s father’s brother, who was imprisoned in Buchenwald for political reasons and eventually beaten to death by the Gestapo in Dresden.

“We reconstructed the last two years of my uncle’s life and his death. What we didn’t know, we filled in the gaps as best as we could,” Raab said. “We wanted to give him voice.”

The book’s title refers to the “stolpersteine” (stumbling blocks), small memorial stones that artist Gunter Demnig has placed throughout Europe, outside the homes of victims of the Nazi regime.

Their research took them to Buchenwald, where they found a record of Raab’s uncle in the archives. Family members didn’t offer a clear explanation for the uncle’s fate, so the couple pieced together what they could from family documents and letters. Many of Raab’s relatives were reluctant to dredge up this history.

When Freestone met Raab’s parents, his mother apologized for the Holocaust but said no one in Germany had known it was happening.

Raab’s father, the former Nazi, had a different perspective. “[He said] almost everybody knew,” Raab said, adding that his father did try to minimize the number of victims. “I remember him saying to Julie, ‘Whatever the numbers are, it was the greatest mass murder ever.’ ”

More information about the book and research is available at www.stumbling-­­­­stone.com.