Thank you to Penguin Group Viking Penguin and NetGalley for providing me with a copy of this title to read and give my honest review. The opinions expressed here are my own.
I will be honest, I had no idea what this book was about. I saw Stiefvater's name on it, knew I loved all her previous works, and decided it didn't matter and I'd give it a chance. I'm so glad I did. It was totally different from what I know from her and a great joy to read.
Normally, historical fiction is not my cup of tea. I struggle with it, especially for the WWII time period. However, this one was totally different from other WWII books I've read. While it does take place during that time period and the basis of the book revolves around what was happening during the war, it was about so much more than that. It was about relationships and how they grow and change, morphing into what you need when you need it. It was also about priorities and putting yourself before others while still showing empathy and care for those who surround you.
The history of the government using large hotels as a house for captured Nazi's in America was fascinating. I knew this happened but I didn't know to what extent. 
June's point of view delves into the daily routines of the hotel, catering to it's guests, and how this is applied to the prisoners of war, because that is exactly what they are. They are treated to top notch service from her staff while still being restricted to what they can have and where they can go. Her connection to the waters that run under and around the hotel in West Virginia speak to the lore that often comes from this part of America. WV is rich with folklore steeped in the paranormal. While the waters definitely give off a paranormal vibe, I will say I never fully understand their presence or what they truly meant for the hotel. They are magical but they are not. They are healing but they also take away. I did understand the waters took from those who chose to submerge themselves: taking the good and expelling the bad to keep the hotel happy.
Tucker's character was my favorite. I loved his history with WV and how he buried it, only for it to grab at him as soon as he was back. His connection with the water is different than June's but not any less important. And the slow burn romance that ensues between the two is expected but comes upon you in bits and spurts. Their friendship grows first and then they find attraction. I was not surprised by this in the least. 
I loved that Stiefvater made this book in several POVs. It was nice to see it well rounded rather than just from June's POV, even though she really did take up about 70% of the book.
The pacing is a bit slow with this. And I will say there were times I was confused by the conversations that were happening. I know much of what was presented was to be mysterious given the nature of the spies involved, but even the idea of the sweetwater was confusing at times. This dropped by rating a bit.
I will say, the one secret with the little girl Hannelore I figured out early on. Not sure if that was intentional or not but it was not a surprise to me at all when it was revealed.
Overall I enjoyed this one. It's not my normal genre but it kept me interested and wanting to turn the pages, especially during the last 30% or so when things really ramp up and start to unravel. If you love historical fiction with a bit of magical realism sewn in, and Maggie's lyrical writing, give this one a try!