Character Analysis
Josef Potocki, a Polish man from an aristocratic family, is Gemma's Prince Charming. What's interesting about this character is that he defies Becca's expectations, and by extension, our expectations as readers.
For one thing, he wasn't Gemma's beau, because Josef is gay. (That's why he was persecuted during the war.)
For another, his "kiss" wasn't a smooch so much as it was CPR, which saved Gemma's life after she was gassed in an extermination camp. That definitely beats making out, given the circumstances. We're just practical like that.
Thing is, Josef is more of a plot device than a character. (If you're feeling fancy, you could call him a deus ex machina because his unlikely appearance neatly solves the novel's mystery.) Still, five full chapters are dedicated to Josef's telling of Gemma's story to Becca, and we do learn a thing or two about the guy along the way.
He doesn't consider himself a war hero, for one thing. "Josef was driftwood, really. He floated through life, making no decisions, no plans. He had drifted into his first love affair in Cambridge, drifted to London and Paris, to Berlin. He had not been able to make plans to leave Germany, so he had drifted into the hands of the Gestapo. In Sachenhausen he drifted into a plot for escape." (26.16)
He describes himself as lackadaisical before the war, painting a picture of a Europe that didn't know what it was about to get itself into on the brink of World War II. Most driftwood doesn't end up facing mass warfare and destruction, but metaphors can only go so far.
As an old man, Josef stays around Chelmno. According to the priest there, who is his friend, Josef "could live anywhere in the world. Like me, he is drawn back by the souls of the dead." (22.93) That may sound creepy, but on the bright side, his decision to stay in a town that held so much horror is convenient for the story, as Becca and Magda find him without even trying.