To nine year old Elisabeth, London of 1642 is full of magic and possibility. She loves to ride with her father as he ferries passengers across the Thames. But one evening he does not return. He has been robbed and murdered. Two years after their father’s death, Elisabeth's sixteen year old sister, Kate, shows Elisabeth a gift she’s received, an emerald ring. She refuses to tell Elisabeth who’s given it to her. Instead she distracts her with the story of the Drowned Girl, who lives underwater waiting for someone who is broken hearted to come near, so she can pull them under with her, leaving a circle of belladonna behind. Soon after, Kate drowns in the Thames. Everyone suspects she has drowned herself. Now sixteen, Elisabeth convinces her friend Phillip to teach her to become a cutpurse. She becomes so skilled that Meg Founder, the most powerful thief in London, requests that Elisabeth join her band. Elisabeth refuses. Meg warns Elisabeth not to cut purses in her “territory.” Despite this, she cuts the purse of a man whom she recognizes as a suitor of Kate’s, Robert Kent. Inside the purse, she finds Kate's ring. Soon after, she discovers an illegal play being performed on the streets of London. Among the players is Robert Kent. Elisabeth disguises herself as a boy and impresses Robert by reciting lines. He invites her to join his troupe. The day of the performance constables sentence all of the players to an afternoon in the pillory. Afterward, Elisabeth hides in her house, ashamed. But Phillip asks a laundress for the Kent family, to allow Elisabeth to take her place. Elisabeth is able to slip into Robert’s room, where she finds a bundle of letters written, she assumes, from him to Kate. The letters are filled with promises, praising Kate's beauty. Elisabeth finds Robert in a tavern and convinces him and his troupe to perform Hamlet. During the play Elisabeth accuses Robert of Kate’s murder. Robert accuses Elisabeth of witchcraft. She is locked into Newgate Prison. Her cellmate turns out to be a childhood friend of Kate’s, Allison, who reveals that it was the alderman, Robert’s father, that Kate loved, not Robert. It was Alderman Kent who wrote the letters to Kate. The truth becomes darker: the night Kate died, the Alderman denied ever loving her. She fled the house after drinking wine poisoned by Lady Kent and an envious Allison. Elisabeth learns that she is to to be drowned as a witch. Robert visits Elisabeth and tells her he tried to retract his accusation, but all he could do was convince the court to hang her rather than drown her. Elisabeth's mother slips her a vial to take just before the guards come for her. The liquid in the vial blurs her senses. She feels the prickle of the rope about her neck, then knows no more. Seemingly underwater, Elisabeth finds Kate. Elisabeth wonders if she is to take her sister’s place as the Drowned Girl, but Kate tells her that for this to happen she must be dead, and Elisabeth is not dead. Elisabeth wakes in Meg's house. Meg tells her that Robert bribed her to pay the executioner to cut her down before she’d died. But it was Phillip who persuaded her to save Elisabeth. Meg reminds her that everyone thinks her dead, so she must go into hiding, even from her loved ones. One night Elisabeth slips to Kate's grave, where she finds Robert. He admits that he followed Kate the night she died. She’d pulled away from him and fallen down the steps to the river. Elisabeth realizes that Kate must have dragged herself to the river’s edge, where the Drowned Girl pulled her into the water. Elisabeth writes her sister’s story into a play, which she leaves on Kate’s grave. Months later, Elisabeth, in disguise, travels with Phillip to an alehouse. There she is amazed to see the her play performed by a troupe headed by Robert Kent. Later, as they travel across the Thames, Elisabeth notices a ring of belladonna lilies floating on the surface of the water. She believes Kate has been heard at last.