Writ in Stone

It's double trouble for Nancy and her friends, when an ancient artifact and a little boy are both suddenly missing.  The artifact is a piece of an old stone marker that may prove that the Chinese were in America eighty years before Columbus.  The little boy is Owen Zucker, a sweetie who Nancy sometimes baby-sits.  Nancy's determined to recover both the artifact and little Owen, but someone's out to stop her—permanently!  Ages 8 to 12.