There are many books out there about World War II. Some are written for children while others are for adults. It is rare to have one crossover to where both audiences find gratification.
The story begins in Krakow, Poland during 1939. The war has affected Anna and her father's lives and they have adjusted. He is still teaching his classes but then is taken. Anna is utterly alone. While waiting in the street for her father to come, a man stops in front of her and asks in several different languages "who are you?"
This is the Swallow Man - as in the bird - and instinctively Anna trusts him. That is not to say he doesn't scare her but there is a quality to him that gives her hope. The Swallow Man begins his walk out of the city and Anna follows him. There are no words exchanged, no gestures but Anna has decided this man gives her a chance at living.
What follows are their adventures wandering the countyside of Poland and into the Soviet Union tracking the invading German soldiers. Not all is fun and games. The Swallow Man teaches Anna the rules of staying alive and he also tries to teaches her about life. The plot becomes less important at this time and the journey seems to turn allegorical. The birds, the "Road", the conversations all help Anna toward an ending. What kind of ending? You must read the novel.
6 Degrees of Reading: Salt to the Sea by Ruta Sepetys, Girl in the Blue Coat by Monica Hesse, The Mystery of Hollow Places by Rebecca Podos.