Started reading this as fictional history, but quickly got sucked in by the utter plausibility and realism of the plot and the imagery. It gives a real insight into what our lives could have been like, but for a few twists of fate and chance.
The reader is not challenged by insane plot devices all too common in this genre, and the spell is never broken by improbable scenarios or unbelievable characters.
The secrets of the plot are delivered without blatant hints, making each chapter an new discovery and each character develops a depth that is not immediately obvious when they first appear in the narrative.
Just when you think you know what is going on, and you start to feel that you know where the story is headed, new threads appear, dragging you off in an unforeseen direction.
This is not the fall of the Berlin wall translated into London, though the metaphor is not hidden, but it is a believable account of the realities of its fictional situation written by someone who was actually there, which, if you read the authors biography, you will discover that he was, and he is.