Tregillis has cleverly blended these genres to produce an original fictional treatment of an alternate world where attempts to produce an army of German supermen (and women) meet their match in Britain's resort to warlockery, coordinated by a secret section in the Admiralty. This is an audacious concept which, on the whole, he pulls off very well. Magic is not without cost - the research efforts of the (real) enemies in the Second World War gave rise to technologies that still threaten us, as, in this book, do their fictional occult counterparts. I particularly liked the parallel developments in England and Germany - both of which start with the recruitment of needy children, that in England done in a much kindlier way than in Germany (at least, so it seems).
This is an entertaining, page turning story, which I have just had to sit down and finish, and I'd highly recommend it. I hope that more is to come from Tregillis.
I only had two quibbles with it. First (and I know I'm about to sound like a huffy pedant) though large parts of the book are set in England, the (American) author hasn't quite, as it were, "localised" things enough. As an English reader that bothered me slightly, but I had to think about the issue quite carefully. I admit (reluctantly) that I can't object to - for example - the use of "sidewalk" for "pavement" or to an idiom like "they turned left onto Shaftesbury" (dropping the "Avenue"). An American author describing events in Britain (or Germany, or Mars, for that matter) is going to use idioms familiar to him. Fine so far. But I think that a different standard applies where an author puts words into his characters' mouths and that he should - for example - take care not to use "gotten" for "got", or pay attention in some of the cases where the forms of verbs apparently differ (I never realised that this was actually the case, but when you see "teared" instead of "tore" you realise how tricky this stuff can get). Equally, I'm pretty sure that a wedding in London in the 1930s could not have taken place in a private garden (I don't think it would be legal to do that even now).
These are only tiny details, but they did - for me - undermine the overall (excellent) effect.
Secondly I was left slightly baffled by a couple of plot strands that seemed to go nowhere. Who was the strange figure with the beard and scar who turned up a at night and vanished into thin air? There was a lot made of him but I didn't understand who he was or what his point was. A loaded gun, on the wall, that was, in effect, never fired. I was also unclear about Gretel's motivation (I won't go into details as they would be spoilers). Maybe these are hooks for sequels - or perhaps I'm just being dim!
Anyway, to summarise, a wonderful book, it deserves to be read widely, I hope that more follow from this author (including, perhaps, a direct sequel?)
Sequel is on its way - The Coldest War - with the third part to come after. Can't wait!