As is the case with any book by Agatha Christie, the story was fast-paced and interesting all the way.
About the book: The Second World War is ravaging the world and in these troubled times, Tommy and Tuppence are feeling sidelined, although they had put in their best efforts while working for the British Intelligence. Now Tommy has been approached to do some sleuthing work but he is to do so without Tuppence. That does not matter to Tuppence, for she joins him in the detective work anyway. Tommy has been asked to search for the German fifth columnists. And the only clue that the two have is the one left by another British agent. The clue is a cryptic message left behind by the agent while on his deathbed (Who killed the agent?). It reads - N or M, Song Susie. It is up to Tommy and Tuppence to make sense of this bizarre message and find out who or what N and M are.
I'm proud to say I knew who the spy was half-way through the book. Even though my parents tried to convince me that the author was hoping the reader would think so - and be absolutely surprised in the end.
I went to a ski resort a week after I finished the book and the environment felt like the story could be re-enacted in that setting. I doubt anyone else there had read the book though - or was even remotely interested in it...