There's Always Tomorrow

Sommer Kappel's world creashed in a single day. Her professor is clubbed by Nazi brownshirts and taken away, she learns she is pregnant and that her boy friend had joined the SS. When her professor told Sommer Kappel that her life would never be the same, she had no idea that she would become a single mother, a British agent, or work with Germany's mathematics genius to create a secret weapon that turned out to be an atomic bomb, or be hounded constantly by a rogue Gestapo agent.
When things were the blackest, she discovered she was pregnant and met a handsome British army officer, who quietly fell in love with her and risked his life to try to rescue her from a Nazi prison in Berlin, regarded by rescue planners as impossible. Along the way, she meets three young women who were to play a pivotal role in her life during Berlin's worst days and share an unexpected gift from an ailing older woman, who held the secret to the secret key her professor had given her on the start of her journey.