Eris Shindanai is a Gearbreaker, a brash young rebel who specializes in taking down Windups from the inside. When one of her missions goes awry and she finds herself in a Godolia prison, Eris meets Sona Steelcrest, a cybernetically enhanced Windup pilot. At first Eris sees Sona as her mortal enemy, but Sona has a secret: She has intentionally infiltrated the Windup program to destroy Godolia from within.