Pam Jenoff - Love and Defiance (#1-3)

The Kommandant's Girl
Nineteen-year-old Emma Bau has been married only three weeks when Nazi tanks thunder into her native Poland. Within days Emma's husband, Jacob, is forced to disappear underground, leaving her imprisoned within the city's decrepit, mouldering Jewish ghetto. But then, in the dead of night, the resistance smuggles her out. Taken to Krakow to live with Jacob's Catholic cousin, Krysia, Emma takes on a new identity as Anna Lipowski, a gentile.
Emma's already precarious situation is complicated by her introduction to Kommandant Richwalder, a high-ranking Nazi official who hires her to work as his assistant. Urged by the resistance to use her position to access details of the Nazi occupation, Emma must compromise her safety and her marriage vows in order to help Jacob's cause. As the atrocities of war intensify, so does Emma's relationship with the Kommandant, building to a climax that will risk not only her double life, but also the lives of those she loves

The Diplomat's Wife
1945. Surviving the brutality of a Nazi prison camp, Marta Nederman is lucky to have escaped with her life. Recovering from the horror, she meets Paul, an American soldier who gives her hope of a happier future. But their plans to meet in London are dashed when Paul's plane crashes.

Devastated and pregnant, Marta marries Simon, a caring British diplomat, and glimpses the joy that home and family can bring. But her happiness is threatened when she learns of a Communist spy in British intelligence, and that the one person who can expose the traitor is connected to her past

The Winter Guest
Life is a constant struggle for the eighteen-year-old Nowak twins as they raise their three younger siblings in rural Poland under the shadow of the Nazi occupation. The constant threat of arrest has made everyone in their village a spy, and turned neighbor against neighbor. Though rugged, independent Helena and pretty, gentle Ruth couldn't be more different, they are staunch allies in protecting their family from the threats the war brings closer to their doorstep with each passing day.

Then Helena discovers an American paratrooper stranded outside their small mountain village, wounded, but alive. Risking the safety of herself and her family, she hides Sam—a Jew—but Helena's concern for the American grows into something much deeper. Defying the perils that render a future together all but impossible, Sam and Helena make plans for the family to flee. But Helena is forced to contend with the jealousy her choices have sparked in Ruth, culminating in a singular act of betrayal that endangers them all—and setting in motion a chain of events that will reverberate across continents and decades.