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Jake Ransom and the Skull King's Shadow (edition 2009)
Jake Ransom and the Skull King's Shadow by James Rollins
References to this work on external resources.
Wikipedia in English (1)
Amazon.com Product Description (ISBN 0061473790, Hardcover)
When a mysterious envelope arrives for Jake Ransom, he and his older sister, Kady, are plunged into a gripping chain of events. An artifact found by their parents—on the expedition from which they never returned—leads Jake and Kady to a strange world inhabited by a peculiar mix of long-lost civilizations, a world that may hold the key to their parents' disappearance.
But even as they enter the gate to this extraordinary place, savage grackyls soar across the sky, diving to attack. Jake's new friends, the pretty Mayan girl Marika and the Roman Pindor, say the grackyls were created by an evil alchemist—the Skull King. And as Jake struggles to find a way home, it becomes obvious that what the Skull King wants most is Jake and Kady—dead or alive.
(retrieved from Amazon Mon, 30 Sep 2013 13:42:01 -0400)
Connecticut middle-schooler Jake and his older sister Kady are transported by a Mayan artifact to a strange world inhabited by a mix of people from long-lost civilizations who are threatened by prehistoric creatures and an evil alchemist, the Skull King.
(summary from another edition)