Gillian Cross 
Born of the Sun [EPUB ebook] 

For years Paula and her father have dreamed and talked about trying to find the lost city of Atahualpa. And now, without warning, Paula is taken out of school and finds her dream come true. Together with her parents and Finn, the photographer, she travels to South America to begin the journey. But as they descend towards the jungle Paula senses that all is not quite as it should be. Why is her father so moody and impatient? And why does he insist that the expedition is being shadowed by sinister enemies? Paula realizes that her loyalty to her father is not enough – she must discover for herself what the truth is about the journey she is making.