I have just finished the book and I can only say that it's quite good and enjoyable. I am Spanish and I can appreciate a novel set in Spain on a vey painful time for its history. I think this gets accross quite well, from a human and non biassed perspective. The character's motivations are quite well drawn, and unlike many other reviewers, I felt quite at easy among its characters. It's true that the main heroes don't seem to have pre-set ideologies, by as you keep reading, they end up taking side. This in itself allows for the book to be an initiation, and in this sense, I find it similar with the Shardlake series, where the hero has doubts, puts himself deep questions about politics, religion or love at the same time that he solves crimes. They have also weaknesses, which makes them more human and approachable. Isn't the fact of questioning part of the search itself? Then it should make sense that he questions everything, including himself.
With regards to the story, it is true that sometimes developements are a bit far fetched, but it's not the first time I see this (and most surely not the last). The trick is to read it quickly and get to the end. Perhaps I could agree that there is a twist too many and the long epilogue was not necessary in a novel, but overall for me the most important part of the book is the atmosphere, the interaction among its characters and their feelings more than the spy framework and the resolution of the story. I take from it the danger and the fear and the important bit is whether they get out, not the how.
In reply to some other reviewers about the irritating spanish quotes in the book, I have only found one dialog where there is an error. It says 'malo' where is should say 'mal', regarding the wheather. And I think they (not that many, really) help in picturing the atmosphere about foreigners living somewhere whith a different language.
But the 'malo' nada, I trully recommend it.