Hide and Seek by Kate Messner

A fast-paced mystery from the author of CAPTURE THE FLAG!José, Anna, and Henry are junior members of the secret Silver Jaguar Society, sworn to protect the world's most important artifacts. When they discover that the society's treasured Jaguar Cup has been replaced with a counterfeit, the trio and their families rush to the rain forests of Costa Rica in search of the real chalice. But when the trail runs dry, new mysteries emerge: Who can they trust? Is there a traitor in their midst? With danger at every turn, it will take more than they realize for José and his friends to recover the cup before it falls into the wrong hands.