"Lady Sandrilene fa Toren knows all about unusual magic-she herself spins and weaves it like thread. But when she witnesses a boy dancing a spell, even she is confounded. To her dismay, Sandry learns that as the mage who discovered the power of the young dancer, she must be his teacher. Before lessons can begin, however, Sandry and her uncle, Duke Vedris, get news of a mysterious murderer stalking a clan of local merchants. The killer employs the strangest magic of all: the ability to reduce essence to nothingness. As the murders mount and the killer grows bolder, Sandry's teaching takes on a grave purpose. For it becomes clear to everyone that the killings can only be stopped by the combined magical workings of two people: the young teacher and her even younger student."
—Back cover summary, Scholastic's 2000 edition.
When her three foster-siblings leave Summersea to travel the world with their teachers, Sandry and her teacher, Lark, remain alone in Winding Circle Temple. After her uncle, Duke Vedris, suffers a severe heart attack, Sandry leaves Discipline cottage to live with and care for him.
While out riding with her uncle, Sandry makes two discoveries: the murder of Jamar Rokat, a myrrh trader, part of the war between organized crime families Rokat and Dihanur, and a boy named Pasco Acalon, whose dancing is visible to Sandry's magical vision as imbued with ambient magic.
Sandry, a newly accredited mage, discovers that one of the responsibilities implicit in her mage's medalion is a duty towards any newly-discovered mage who has no teacher. When she finds that ambient dancing magic is so rare as to be unheard of, she is forced to teach Pasco to control his magic himself, while Lark puts her in contact with Yazmín Hebet, a non-mage dancer and an old friend of hers who takes Pasco as her student. Between the two of them they must teach Pasco how to dance spells and convince his strict family of harriers, Summersea's local police, that such a seemingly-frivolous education is necessary.
When the perpetrators of the Rokat murders are discovered to be using Unmagic, the rare and deadly counter-magic that swallows energy and kills those who use it, Sandry and Pasco find out that they are the ones best suited to capturing the murderers. Sandry, the only known person with the ability to spin pure magic, spins a net of unmagic and Pasco dances the murderers magically into it. However, he is caught in the net. Sandry was forced to kill the murderers to save Pasco. With the murderers dead, Sandry takes on new responsibilities at the Duke's Citadel and leaves Discipline forever.