Each summer, Edward and Katherine Shaw visit their grandmother, Eleanor, who, with a knack as a storyteller for talking about legendary lost cities, unexcavated civilizations that are still hidden, and other fabled sites and uncovered mysteries, at her cabin. However, this summer might be their last! Due to failure to pay property tax, Eleanor's cottage is at risk for repossession! Having found out that Eleanor's deeply in debt and in danger of losing her home, both Edward and Katherine, learning about their grandmother's financial problems, attempt to save Eleanor's house (and the rest of the neighborhood) from foreclosure. And in doing so, they discover an old treasure map that takes the two of them on an adventure to unearth the long-lost fortunes of Atlantis and El Dorado, while being pursued by their cousins, a family of con-artists who are after the treasure, as well, and try to sabotage their efforts to save Eleanor's cabin!