In the land of Barracks, the economy thrives on the barter of their citizens' most precious commodity—a human heart. Each year, the Heart Reign festival is thrown for those who have become of age to trade their hearts for their deepest desires. And this year is Adelaide Tye's year to trade. After despising Heart Reign for years, Addie endures her Extraction and discovers that her heart isn’t gray and dying, like all other hearts in Barracks, but bright red, alive, and teeming with power. With a warning from the extractor of hearts, Addie rushes through Heart Reign to make her choice—trade her heart to Schism, the monster who took her brother years before, or go in search of the Mender—a mythical man said to purify hearts and save her own heart. Either decision will rip her away from the one man who has always been by her side. Knowing there is only one real choice to make, Addie jumps through Schism’s red door and is thrust into a dark and dangerous realm where she is faced with making a trade she may not survive. For fans of Stephanie Garber's Caraval and ABC's Once Upon a Time.

After finding out she is the Bellata-the prophesized warrior meant to save Decim-Addie, along with James, returns to Barracks to unite the Twelve Magisters. But as she discovers her old home in ruin, Addie stumbles upon Silas and Nana, the only people left in Barracks. As Silas explains what happened, Addie remembers the special gift Eman entrusted to her. She gives the gift to Silas, only to learn that he's the young blacksmith who fought through the Seven Choices, making Addie unsure of how to react to her old friend. Dodging an attack from Schism, and another deadly ally to Ophidian, the group finally makes their way to Ramni, where a familiar face joins them-one Addie never wanted to see again. If Addie can't learn to balance her new power, successfully unite the Twelve Magisters, and figure out what's going on with a new voice in her head, Ophidian will destroy all the twelve lands ... And she'll never know who is capable of betrayal amongst her friends.