I just happened to read these two books this year. I did not intentionally read two books with such similar settings and subject matter.
The Book of Boy is about a boy who joins a religious pilgrim (older man) on a journey through plague ridden France to hunt for religious relics on their way to see the Pope in Avignon.
Between Two Fires is about a strange girl who convinces a disgraced knight (older man) to accompany her on her journey through plague ridden France to see the Pope in Avignon.
Both books include a lot of Christian mythology and fantastical stuff. There are still a ton of things that set these books apart -- I just find the similarities and the fact that I read them not knowing about these similarities to be interesting.