With the Dark Queen gone, a new villain emerges from the shadows-Doctor Zero, who's discovered how to turn the world soulless. Riley Stark knows the Sentinels can't defeat him on their own, so she frees King Bane and the Renegades from jail, conspires with new soulless allies, and turns her back on her own people to save Caleb. As the Sentinels come to resent her, Riley has no choice but to take soulless help to stop Doctor Zero.