As monsters and gods descend on San Francisco in battle-ready droves, these teenage heirs of Medusa must seek the truth and fight to claim their immortal legacy. Greer has mastered her gift of second sight, but when a god starts playing with her mind, can she fight back to protect her sisters' mission? Grace wants to trust her adopted brother Thane, but his past is full of dark mysteries. Will Thane's secrets put the girls in even more danger? Gretchen's job as huntress is no longer cut and dry, now she has got to know some of the beasties in the abyss. Can she come to terms with the responsibilites of her birthright?