But the heroine of "City of Women" by David Gillham, has secrets. Consumed by thoughts of her Jewish lover, a chance meeting with a girl in a movie theater leads to her gradually being caught up in a network of people helping Jews flee to safety as she navigates between what is safe and what is right.
Gillham, a debut novelist with a passion for history, said the impetus for his book came from asking what he – or anybody – might have done in a similar time and situation.
"It's very easy to have a moral position when your life is not threatened. I wanted to put that pressure on and explore how people reacted to it," he said in a telephone interview.
"But it's more of a personal reaction on her part than a moral decision, and that's one thing I wanted to explore too - how people make these moral decisions."
In Sigrid's case, one spark is her decision to lie to Gestapo soldiers about the young woman sitting next to her in a movie theatre, a move that comes more from her resentment of their bullying stance than any spirit of helpfulness.
The woman, Ericha, is part of the group hiding Jews from the Gestapo, and Sigrid slowly becomes deeply involved with them, eventually helping a mother and two children that she starts to suspect may be the family of her lover.
Gillham said he felt Sigrid was much like Berlin, once very passionate, but now oppressed, and that this guided many of her choices through a slow evolution.
"Her life's exciting, she feels that all the excitement comes back. Maybe she realizes that she's in a dangerous situation and feels like she's taking some stance, but it's the excitement that drives her," he said.
"By the time she realizes the lines that she's crossed, she's already crossed them. Then of course she has to face the hard edge of things, when people she loves betray her, and what will she do for love, and what will she do to protect her own life and the lives of others."
Long interested in World War Two Berlin, Gillham, who trained as a screenwriter in his 20s, said he originally wanted the story to be only about women as a reflection of Berlin's largely manless state, with everybody off fighting the war. Sigrid came from an old, unfinished piece of writing and "took over" the narrative.
Nights cowering in cellars during air raids alternate with gray, cold days as Sigrid goes to and from her job, broken by the growing tension of her secret work and enlivened by memories of her lover, Egon, who has vanished.
Gillham said he feels the key to writing interesting fiction is characters that have secrets they reveal to him as he writes, and this book, he said, was full of them.
"Egon - for instance, when I first developed Egon I had his personality but I didn't have any of the business about his family, about his wife and children and who they were and who they might be," he said.
"He re-invents himself every time you see him, and the stories he tells - you never know if they're true or not."
A veteran of years of writing before selling his first novel, Gillham said persistence is the key to success.
"You just stay at it and don't lose faith in your abilities," he added.
"Then you'll find in fact that if you've got the ability to write, you're a better writer than you were a few years ago and you create the piece that everybody wants to read. Hopefully."