It started out in an interesting way. A child has been raised on his grandfather's stories of moving from Poland to England as a child, growing up with children who had strange powers, and fighting monsters who wanted to kill them. When he is older he realizes that really his grandfather moved to England from Poland to escape the Nazis, and they were the "monsters."
Except of course the kid finds out it was all true and blah blah blah he goes to England and it turns out he has strange powers and has to fight evil. So his grandfather was persecuted for both reasons, and at that point the comparison started to get a little tacky. The monsters who are after them are called "hollowgasts" which sounds like "holocaust," and I think that was deliberate. I don't mean that I thought this was a horrible thing or that no one should use the holocaust in fiction, but I really didn't like how it was handled very much.
I actually thought it would be really interesting if it had been a different book entirely -- if the main character was never actually sure if his grandfather had been making up stories or not. Maybe if he even wasn't sure about his own sanity, which is called into question at one point in the story. Because at the end it was just this sort of bog standard story about a kid who finds out he's not an ordinary human and has to battle evil.
Of course that would have been a completely different book, and I did realize from the beginning that that wasn't where this book was going, but I'll just say I liked the first part a lot better than the second part.
The central motif of the book is that the author used "found photos" to inspire him for the story, mostly eerie old Victorian ones, and the photos are printed in the book. Except I read it on the Kindle and couldn't see them so well, which probably didn't help my enjoyment of it.