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 Tuppence Beresford. Their mission: to seek out a man and a woman from among the colorful guests at Sans Souci, a seaside hotel. But this assignment is far from an easy stroll along the promenade—N and M have just murdered Britain’s finest agent and no one can be trusted.