Karigan's will proves no match for the Rider's call; ghostly hoofbeats sounding in her mind, visions of the freedom of the open road, all calling her back to the king's service as a GREEN RIDER. Karigan resists it, but when she wakes up to find herself - in her nightdress - on horseback and halfway across the country, her destiny is clear: she is a GREEN RIDER.

As she discovers, it's not a good time to be called to serve. For a thousand years the D'Yer Wall, a physical and magical barrier protecting the land from the ancient, corrupted Blackveil Forest, has held. For a thousand years the forest, an arboreal prison containing one of Sacoridia's greatest enemies, has been quiet. Not anymore. The wall has been breached, unnatural, lethal creatures are finding their way into Sacoridia, a dark sentience is stirring and the GREEN RIDER magic itself is failing. And in the midst of it all, Karigan is about to be called to her duty...