Astrid Lamb could care less about being a witch. She'd much rather lead her gang of teenage miscreants into battle against their rival groups. Unfortunately, her 16th birthday is approaching, and she'll be expected to learn magic and assist her mother in the family trade. But when the elder witch is arrested by the aristocratic Magicians' Guild for performing illegal magic, Astrid's world is flipped upside down. She learns that her mother is more than a simple brewer of potions - she is the leader of the Left Hand, a revolutionary group that is dedicated to overthrowing the Guild.

The little witch will have to team up with an astonishing assortment of allies: an airship captain who smuggles magical contraband, a sympathetic magician and his snobby son, and a pair of sorcerers from New York. But even with help, the situation is grim. If the Guild can extract the information that Astrid's mother holds, all will be lost. How can a kid from the slums possibly stand up against a thousand-year-old institution?