The Secret of the Stones (Sean Wyatt Historical Mysteries)

Sean Wyatt's learns his best friend has been kidnapped while working on a secret project. Sean and his new acquaintance, Allyson Webster, embark on a mission to solve a series of ancient clues they he hopes will lead to whoever kidnapped his friend. The riddles lead them on a dangerous chase through the southeastern United States and to a four thousand year-old secret that is bigger than anything they could have ever imagined.