N or M? by Agatha Christie (UK edition, paperback) - 9780007111459

Set during the dark days of World War II, Agatha Christie's N or M? puts two most unlikely espionage agents, Tommy and Tuppence Beresford, on the trail of a pair of Nazi spies who have murdered Britain's top agent. World War II is raging, and while the RAF struggles to keep the Luftwaffe at bay, Britain faces a sinister threat from "the enemy within"--Nazis posing as ordinary citizens. With pressure mounting, the intelligence service appoints two improbable spies, Tommy and Tuppenc...