There are many books dealing with the period 1925 - 1955. The generation who grew up after the War to end all Wars, lived through the Depression, the Communist / Fascist struggle that ended in WW2 by way of Spain. The first half of this book is just one more of these books - four Scots brothers of which one is in the FO and a Russian spy, one a Nazi fellow traveller, one goes to colonies and does well, and the narrator who is a journalist so he can see interesting bits needed by the story.
But the second half is an excellent bringing together of the various strands, not just in a plot but by way of superb writing that makes us feel it in the characters. The result is to give a wonderful sense of what the 1945 - 55 period meant in France, Germany, Britain and then Europe.
p 191 for an acute summary of Churchill -- the man who could face one reality but not a second.