"Greetings Millie, do not be afraid, I am your Companion." So begins the adventure of a lifetime for Millie and her twin brother,Oliver. Will they succeed in finding the Cornerstone for their mysterious new friend? What is a Cornerstone anyway? Millie is a fiesty, independent girl with a strong personality and an agile mind and she is used to people having high expectations of her, but this is a difficult assignment even for her! How had an innocent family visit to an antique shop led to this? Unfortunately they are not the only ones who seek this strange object and they find themselves part of a centuries old struggle for supremacy. When ancient secrets are finally exposed, however, the twins are placed in terrible danger and they must fight to survive.