Puca has one last quest for Mercia before she can go save Nick and it's a doozy. The Grimoire of the Witches of Puca. The last person to see it was Pil. Both Sarah and Puca believe the grimoire's location is locked somewhere in Mercia's mind. The only way to find it is in the past and magic can't be changed. The power of an oath will eat you away bit by bit until you disappear or succeed and Mercia doesn't have much left to feed it. Janice is in Lanta and Sarah intends to free him at all costs. But she can't go to the surface without an army. Sarah sealed all the entrances to the surface. The Fae were chased down into These Hallowed Hills its time to come out, come out, where ever you are, and fight. The CDC is just the first battle. Jacques would never put all his eggs in one basket and neither would the GOVs. Sarah has discovered a missing piece to the stone puzzle hiding in plain sight and it's the answer to ending the war for good, but only if Mercia comes through.