The Carter Girls and the Battle of Frontenac Island

It doesn't look like anything special. The medallion that Therese and Jenna Carter unearth is old and chipped, its raised markings starting to wear. Nothing but a worthless old piece of junk. But if it is as worthless as it seems, why has someone kidnapped their grandfather? And why is he demanding the medallion as ransom? With more questions than answers, the girls are led to a mysterious city full of mythological creatures where they find themselves imprisoned and sentenced to death simply for being human. They learn that the medallion is immensely powerful and there is far more at stake than just their grandfather's life. Millions, perhaps billions, will die if it falls into the wrong hands. Therese and Jenna must keep that from happening at all costs, but what can the Carter sisters do when they are helpless to save even themselves?