Agatha Christie said she liked Tommy and Tuppence best of her protagonists, so I decided to read them all in order. N or M? is the third. Unfortunately, they tend to be espionage novels, which are not her best even though Tommy and Tuppence are fun.
It’s 1940, and both Tommy and Tuppence are frustrated because no one wants them to help in the war effort. Tommy at 49 is considered too old for intelligence work. However, shortly after he makes another attempt, he’s called on by a Mr. Grant who has an independent operation for Tommy only.
England has become infiltrated by Nazi sympathizers in all levels of government, which is why Mr. Grant wants someone from the outside. He has information that either N or M—both German spies, one male and one female—is at the San Souci rooming house in Leamington. Tommy is to pretend to have got a boring job in Scotland then go to Leamington and check into the San Souci. He does so, only to find one of the guests is Tuppence, who has eavesdropped on his meeting with Mr. Grant. So, pretending they don’t know each other, the two begin investigating the household.
I thought that Tommy and Tuppence were a little dense about the identities of the spies. I knew who one was almost immediately. However, this was the usual romp with some adventure and risk to our hero.
whatmeread 
I’ve still only read the first two Tommy and Tuppence books, so this will be the next one I read. I usually find Christie’s espionage stories entertaining, even if they’re not always her best.
This one is.
It has been a while since I read these, so I don’t remember much about the story, but I adore Tommy & Tuppence!
Me too!
I have just entered into reading all (him) of Agatha Christie’s work and saw this in the list. I have noticed they are good listening to. Otherwise, I am not so fond of audio books, but works well here. Will soon come to this one.