The Message in the Painted Rock

Summer vacation for Arthur and Marya takes a very strange turn when a weird old man with a long white beard draws the two friends into an ancient mystery that they must solve in order to recover a magical artifact from the distant past. They soon learn that they are not the only ones who seek this relic; closing in on them are powerful evil forces that will stop at nothing to get their hands on it. With help from some very unlikely sources, Arthur and Marya unravel clues that lead them to their goal, only to discover that it is protected by creatures they never imagined. When they find themselves deep underground, with time running out and with nothing to rely on but their own courage and trust in each other, the teenagers must vanquish inhuman forces if they want to get out alive.

Paperback book by Tom Blanton.