Pedro and the Magic Marbles

The annual visit by Pedros grandparents coincides with his discovery of special marbles found in rocks brought home by his father from the marble mine where he works. The village of Marbleville and the mine there hold some very strange mysteries, where in the past whole families just disappeared without trace. When Pedro shows his grandmother the marbles he has been finding, she decides it is time to open some envelopes entrusted to her many years previous by the mother of the present mine owner. What she finds out leads the family on an adventure into the past.