After her father dies from cancer, seventeen-year-old Olivia Campos has two things in mind: obsessing over his research of Arthurian legend, and the inscribed key he gave her seconds before he passed.
When she embarks on a trip from her home in Brazil to Wales to see a special Arthurian exhibit, she discovers the same strange words from the key written on Excalibur's blade. Mesmerized, she touches the sword, but it transports her back to the fifth century, where she materializes in front of the young sorcerer, Merlin- at the exact moment he thrust Excalibur in the stone.
Realizing that Olivia was brought by magic and destined to aid Arthur, Merlin agrees to help her return to her own time in exchange for her assistance securing Arthur's reign. However, when they finally cross paths, Olivia learns Arthur is nothing like the noble hero she admired from her father's stories-he's selfish, stubborn, and annoying.
Armed only with her knowledge of Arthurian stories, she dives into the court's intrigues, determined to fulfill her end of the bargain with Merlin. But in doing so, she discovers another side of Arthur, and they grow closer than her heart deems safe. But to return to her family, Olivia will have to risk everything to protect the once and future king-or stay lost in Camelot forever.
In the epic conclusion to the Devil's Deal series, Freya has one final chance to discover the full potential of her own power, and to use it to restore balance in the universe - once and for all. After the destruction caused by Roisin, Ferya and Torix come to terms with their losses and mistakes... And prepare for a final battle that will change everything.