This book was good but also hard to read at times. The book alternates between two storylines and perspectives - Evelyn, a spy during WWI, and Charlie, an unwed pregnant 19 year old searching for her cousin in a France that's still recovering two years after WWII. Evelyn's storyline was harder to get through compared to Charlie's. This is mostly because you know the entire time that things are going to end badly due to not only it being WWI (a time that's hard to read about period) but also through Charlie's perspective. This kind of anticipation bordered on dread at times - so yes at times it was hard to read.
Charlie's storyline was better despite some parts not making sense for her character and once she stopped being all "I'm not like other girls" every few paragraphs. I did really like Finn, the Scottsman with a record and WWII trauma, though (this comes as a surprise to no one).
Overall this book was a good one. I liked that the author used a lot from actual history - including characters and quotes. That made the book pretty interesting and grounded in reality - something a lot of historical fiction cannot claim.