After Julian Vance is imprisoned, Nora thinks it's all over. But then a series of new drownings emerges, each mirroring Julian's methods. The killer appears to be a woman with a Seven-Ring Seal tattooed on her wrist. Nora and Ethan discover that Julian has been using Morse code to send messages from prison and train an apprentice: prison guard Lucas Crain. Lucas directs his girlfriend, Amanda, to carry out the murders on the outside. But the true mastermind is Julian's psychiatrist, Isabel Crayne—and behind her lies a far older name: Corvus.
