Moss hates her life. As the daughter of the Executioner in the Tower of London, it's her job to catch the heads in her basket after her father has chopped them off. She dreams of leaving, but they are prisoners with no way out. Then Moss discovers a hidden tunnel that takes her to freedom, where she learns that her life isn't what she believes it to be and she doesn't know who to trust. Her search for the truth takes her on a journey along the great River Thames. Could the answers lie deep in its murky depths?