I'd never heard of "Mary Burchell" or the real girl behind the pen name, much less the use of opera to cover international rescues in war, so this was a fun discovery. The exploration of the sister relationship without it being paired with romantic relationships was refreshing for a WWII novel, though I definitely wanted more detail in their family (the brothers/sister-in-laws only make token appearances, and the parents are more caricatures). Structurally, the use of tiny named vignettes rather than typical chapters made the narrative disjointed. Still, this was an important story that I enjoyed learning.