Imagine a raven appearing out of thin air and guiding you to an exquisitely carved icon that glows with ancient light and pulses with shamanic power. This is how the adventure begins for Nadia and Aidan Shaw, thirteen-year-old twins, who live in idyllic Cold Spring, New York, on the banks of the Hudson River. Armed with the power of the Ravenstone and their own special gifts, they plunge back to the fifth century, where they encounter Native Americans, ancient Celts, warring princes and a shape-shifting raven. Determined to retrieve a now-extinct healing plant, they must depend on their...