"Magic's Promise" is a fantasy novel by Mercedes Lackey, part of the Valdemar series. The story follows a young girl named Mags, who discovers his magical abilities and embarks on a journey to understand his powers and place in the world. Throughout the narrative, Mags encounters various characters, including Companions, magical horse-like beings that bond with chosen individuals. The novel explores themes of friendship, loyalty, and the struggle between good and evil, as Mags learns to harness his magic and fulfill his destiny.