Geronimo's adventurous sister Thea narrates this fabulous adventure that's packed with action, mystery and friendship. In this amazing adventure, Thea's friends the Thea Sisters head to Peru, where a good friend of Paulina's is in danger. There, the five mice climb the Andes mountains in search of a mysterious treasure that's hidden in the Secret City of the Incas. Readers will love following the clues to help the Thea Sisters solve the mystery.