All her life, Moss has lived in the Tower of London with her father, who serves as the executioner for King Henry VIII. Prisoners condemned to death must face Pa and his axe—and Moss catches their severed heads. Her father insists he has no choice: if he leaves the Tower, he will be killed. But Moss can't bear to be the executioner's daughter any longer. When she finally finds a way out of the Tower, she discovers the river holds more dangers than she imagined—including the Riverwitch's curse. The Riverwitch once helped Moss's family in exchange for a terrible bargain; now she expects Moss to pay the debt.