Young sleuths Jack & Rose Archer must save their crooked Uncle Esteban from Nazis, Incan magic, and an army of ravenous vampire monkeys.
Whenever they are not risking their lives to settle the hash of crime kingpins, con artists, black magicians and other assorted raving maniacs, Jack and Rose Archer live quietly on a houseboat moored in Manhattan's harbor. As this adventure opens, their rich socialite parents are touring Europe. Jack spends the days tinkering with his Nemo style diving suit while Rose practices her ninjitsu on straw dummies. This idyll gets shattered by the appearance of an obese man in a white suit with a thick Cuban accent who claims to be "your considerate Uncle Esteban." Realizing that crooked "Uncle Esteban" is trying to pump them for information on an one of their father's old archaeological digs, the children slyly cat-and-mouse the old rogue. But the situation turns ugly as Uncle Esteban gets kidnapped by Nazi frogmen and taken aboard a U-Boat. Jack and Rose trail the kidnappers to the steamy jungles of Peru only to find to their horror that the Nazis have already located the treasure -- a gold Incan demon mask -- and are using its evil magic to create an army of vampire monkeys.