The Hardys and friend Callie Shaw are off to Washington, D.C. Callie finally has the chance to meet her Parisian pen pal, Madeleine Berot, whose parents have been assigned to the French embassy. But when Maddy is caught shoplifting, Frank and Joe suspect that there's something rotten in the state of French diplomacy.

Determined to get to the bottom of the Madeleine Berot mystery, the Hardys find themselves caught in a web of international intrigue. They take of on a tingling chase through the nation's capital, pursuing a gang of continental con artists. In a case of D.C. deceit, it's up to Frank and Joe to nip the caper in the bud!