N or M

" N or M? " is a detective novel by Agatha Christie featuring her famous detective duo Tommy and Tuppence. It was first published in 1941 during the height of World War II. The story is set in 1940, and the main characters are recruited by British intelligence to track down two German spies operating in Britain under the code names "N" and "M".

Tommy and Tuppence, now middle-aged, are happily married and retired from their detective agency. They are approached by a British intelligence agent, Grant, to help track down the German spies, as the intelligence agency believes that the spies are planning to carry out a major operation in England. Tommy and Tuppence, who are eager to do their bit for the war effort, agree to help.

Posing as a couple on holiday, they infiltrate a seaside guesthouse called Sans Souci, where they believe the spies are staying. The guesthouse is run by the sinister Mrs. Perenna, and they soon become suspicious of her and her guests, who include a mysterious doctor, a wealthy American couple, and a pair of middle-aged sisters.

As they begin their investigation, Tommy and Tuppence discover a series of clues and red herrings that lead them on a dangerous trail through London and the English countryside. Along the way, they must use all their ingenuity and resourcefulness to avoid detection by the German spies and Mrs. Perenna.

As the investigation progresses, the couple realizes that they must find the spies before they can carry out their plans to sabotage Britain's war effort. The tension builds as they race against time to uncover the identity of "N" and "M" and stop them before it's too late.

Overall, "N or M?" is a gripping and suspenseful mystery novel that highlights Christie's skill at creating complex plots and memorable characters. The novel's wartime setting and themes of espionage and patriotism also add an extra layer of intrigue.