Famous sleuths, Tommy and Tuppence Beresford, become involved in one of their most baffling cases in the tense early days of World War II...Hitler s two most trusted agents are in England. N is a man... M is a woman. Both are masters of sunning, decption... and murder...In the unlikely setting of a seaside boarding house inhabited by an innocent-seeming collection of boarders, Tommy and Tuppence get on the trail of a ruthless scheme involving espionage, kidnapping and killing... N or M?