The Grand Illusion

I was interested and intrigued by the theme of this book, especially as it is based on a real department of the War Office during WWII when people from various walks of life, (performers, artists, writers, magicians etc), were recruited in an attempt to come up with schemes and plots to try prevent the invasion of Britain by Hitler's forces.
The book started off well and I quite liked the Daphne-Jonty team. It is quite weird looking at the way they are recruited and go along with everything asked of them with modern eyes. They are all so unquestioning but I think that, at that time, people didn't question those in authority, especially if those in authority were educated, from a higher class and wearing a uniform. It would have been deemed unpatriotic to do so, however bizarre the request.
I did struggle as the story unfolded and was quite confused by the end. Are we expected to believe that sorcery was used? Were there mind-altering drugs in the chalice? Had the german soldiers been 'allowed' to land in order to see the ceremony and report back? It was just supposed to be a performance like one of their magic tricks. The ending seemed a bit rushed and unresolved as Daphne is stood down and isn't part of the debrief. I understand that the book is set to be part of a series so it will be interesting to see what happens next and whether any questions are answered.