N or M? is a detective novel by Agatha Christie, first published in the US by Dodd, Mead and Company in 1941. and in the UK by the Collins Crime Club in November of the same year. The novel is the first to feature the mature versions of her detectives Tommy & Tuppence, whose previous appearances had been in the adventure The Secret Adversary (1922) and the short story collection Partners in Crime (1929).
