This is a tale of Germany trying to win the war. It's a good thing they have Sherlock's daughter there to figure things out.
Minotaur Books and Edelweiss let me read this book for review (thank you). It has been published and you can get a copy now.
First the blue diamond is stolen, then some secret maps. The diamond was well-guarded and shouldn't have been stolen. That leads to the suspicion they must have a traitor in the guard.
The beginning of the book is slow reading but as you go on it starts to get exciting.
The Germans have planned it out good but didn't expect Sherlock's daughter to be involved.
There are multiple answers but when they kidnap Watson, she really puts her mind to it.
It's an interesting mystery.