Karigan may have heard the First Rider's call, but she's not about to let it take over her life...or at least that's what she thinks. She swore to complete a dying man's mission - to deliver a sealed letter to King Zachary. Now that task, more dangerous than she could have imagined, is complete and her work is done, Karigan wants to leave the dangerous world of tainted magic and ancient magicians behind her and return home. Exhausted in both body and spirit, she plans to return to her quiet life and her father's business.

But it 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 1,000 years the D'Yer Wall, a physical and magical barrier protecting the land from the ancient, corrupted Blackveil Forest, has held. For 1,000 years the forest, an arboreal prison containing one of Sacoridia's greatest enemies, has been quiet. Not any more. 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....