A mysterious letter from an old friend of her father's brings Katie and her brother Pete to Egypt, where they encounter a conspiracy involving theft and terrorism.

Katie and her brother, accompanied by friend and secret agent Jane Weston, embark on a journey to the Brazilian jungle after an urgent message from their parents already in Brazil, where Mr. Thompsen is writing about the ecology of the Amazon.

When long-lost Grandpa Thompsen suddenly invites them to his South Seas island, Katie and her family find that Grandpa's colorful past turns their visit into a dangerous adventure.