I knew this was a retelling, an alternate history of WWII with a fantasy bent to it, and rather expected a Captain America feel. I was very wrong on that count. Gretel was thoroughly enjoyable as the main villain, and I still picture her in my mind as a young flighty woman who loves to read poetry and pick wildflowers and carries a secret torch for a young man. Never mind that she's completely insane and is willing to sacrifice the world for her own gain. 
 Actually, I was really impressed with the depiction of England, which has fallen very very far, indeed. The bitter seeds from the title could entirely be planted by those plucky English chaps. 
 I particularly liked the mix of quasi-Cthulhu Eidolons as a substitute for demonic contracts and the more traditional stick-those-wires-in-the-brain awakenings. I mention these things first because I found them fun, but more than that, I really enjoyed the story and the characterizations. I kept wanting to see a secret agent book with magic and sci-fi elements in WWII, but what I actually find is a heart-felt analysis of hard choices, coping mechanisms, regret, loss, and a deep horror at the situation. Mr. Tregillis could easily write a straight novel without any fantasy elements and be perfectly at home, but he succeeds in making a great sci-fi/fantasy novel. 
 I know it is just beginning, of course, and so I'm going to sink my teeth in the next, now.