N or M? (পেপারব্যাক)

It is World War II and Britains best secret agent has been murdered. The murderers are Nazi agents, known only as N and M, and could be anyone. The only clue points towards the sleepy seaside village of Leahampton and its busy guesthouse, Sans Souci.

Tommy and Tuppence Beresford, Britains most unlikely spies, accept the mission to find N and M. No one can be trusted.