Sixteen-year-old Lia Milthorpe must journey to the uncharted isle of Altus to continue her search for the missing pages of the Book of Chaos — the pages that could tell her how to end the prophecy that has turned generations of sisters against each other. But the journey will test more than just her courage, it will also test her loyalty to her beloved boyfriend, James. Meanwhile, twin sister Alice will stop at nothing to reclaim Lia's role as the Gate. And that's not the only thing she wants from her sister: there's also Lia's true love. The outcome of their battle could have consequences of Biblical proportions and, in the end, only one sister will be left standing.

Now that Lia has found the missing pages of the Librum Maleficii et Disordinae, or the Book of Chaos, the end of the Prophecy is in sight. While Lia tries to save James from Alice's sinister grasp, she unlocks the prophecy's final mystery and a caveat that may put an end to any hope of ending the prophecy; to close the Gate to the Beast forever, Lia must convene in an ancient ritualistic ceremony with all four keys at Avebury. But that's not all. Alice, as Guardian, must be there as well.

Without the Keys, something terrible will happen. Something that cannot be undone. And with them, I might bring an end to the riddle of the Prophecy and my strange part in it. If Alice and I are on conflicting sides of the Prophecy, the Keys would be dangerous in her hands. Which means I have to find them. And I have to do it before my sister. This is the story of sixteen-year-old Lia Milthorpe's quest to discover her role and her twin sister's in a powerful prophecy that has affected twin sisters for generations. But nothing can prepare her for what she discovers — about herself, about her family, and about the danger that goes from haunting her dreams to becoming her reality.