Young heroine Karigan hardly has time to regret being expelled from school (for dueling) before finding herself committed to the desperate errand of a murdered Green Rider.

The Riders are an elite messenger corps using both horses and magic; the message is a terrible warning. Bad things from bad places are invading this fantasyland, their presence being only part of a devious, sorcery-aided human struggle for the throne. Karigan's wild ride is beset by a variety of enemies, but aided by her own developing talents plus certain strange allies.

These include the tormented ghost of the dead Green Rider himself--still pierced by and trying to resist the chief villain's black arrows that ensnare the soul. Delivering the message to a suspicious court is only half Karigan's job: can it be interpreted in time?