Islands of Intrigue

Islands of Intrigue is a Nancy Drew and Hardy Boys Supermystery crossover novel, published in 1996.

Plot summary
Alexis Constantine, the daughter of a Greek shipping tycoon, is kidnapped by a shadowy figure, after she invites Bess and Nancy to head to Greece on their world-class yacht. Meanwhile, the Hardys arrive in Greece as well, to hunt down a U.S double agent who is accused of smuggling out a cluster of Phoenix missiles from his homeland base. Working together, the gang head out on a cross-country trip, trying to discover the true solution to the problem at hand.