James Rollins 
Jake Ransom and the Skull King’s Shadow [EPUB ebook] 

Three years ago, a mysterious package arrived for Jake and Kady Ransom. Inside were two halves of a Mayan gold coin, their mother’s sketchbook and their father’s notebook. But their architect parents failed to return from an expedition to the site of a long-lost Mayan civilization. Now Jake and Kady are plunged into a terrifying adventure. Someone is very interested in what’s happened to their parents. And in Jake and Kady themselves. So begins a journey into a world of dangers both ancient and modern. Can Jake and Kady survive long enough to solve the mystery?