Parts of this were very engaging and I learned about a variety of initiatives and actions I'd never heard about. But I had trouble with the bits where the author imagines or theorizes about what may/might have happened at a given moment. She always makes it clear when she's doing this, but the specificity of those moments really felt like a novel rather than an examination of a past possibility. It drew me out of the story every time, because it felt like playing make believe with real peoples' lives. 

Aside from that, I felt like it went a bit hard trying to sell readers on the non-battlefield contributions. Like, they were obviously crucial, but there are several times where the author mentions them as though they're the only reason the Allies succeeded, which felt kind of over the top to me. I'm not sure it's a contest between people dying on the front lines and those risking their lives to provide the intelligence for military movements, and it sometimes read like the author kind of thought it was. 

Anyway, these are perhaps small pieces of the overall work, but they're why I didn't find it quite as engaging as other nonfic I've read about WWII. Still worth a look if you're curious about the spy/intelligence part of that history though.