N or M

This atmospheric story, set during WW2, finds the now mature Tommy and Tuppence Beresford doing what they do best—having an adventure. These two unlikely spies help to defend their country by trying to rout out two highly placed Fifth Columnists. When Tommy is asked by the British Intelligence Service to go and stay at the Sans Souci guest house he is astonished to see Tuppence there. The mission: to identify which of the other guests is N and which is M....