The following version of this book was used to create this guide: Aveyard, Victoria. King's Cage. Orion Publishing Group, 2017.

Norta is a nation divided between the power-hungry, silver-blooded ruling class and the exploited red-blooded lower class. Silvers rule over Reds using special abilities granted by their blood, a dynamic challenged by the discovery of “newbloods” – Reds with Silver abilities. King Maven Calore, the ruler of Norta, holds newblood Mare Barrow captive, accusing her of leading the Red resistance group called the Scarlet Guard. He allows Samson Merandus, a Silver whisper with the ability to read and manipulate minds, to interrogate her and he forces her to relive the death of her brother, Shade. She attempts to escape and fails. Meanwhile, in an underground military base, Cameron Cole works with the Scarlet Guard to try to free Mare and advance their cause. Cameron pushes the exiled prince of Norta, Cal, to help her save her twin brother from conscription in Maven’s army, but her requests are refused.

Maven tries to gain Mare’s trust and she learns that he loves her. She gains insight into his life, learning that he was manipulated by his mother, Queen Elara, and is unable to love anyone else. She learns that he makes his decisions on a throne of Silent Stone to prevent any other whispers from influencing his decisions, and that he is putting off his marriage to Evangeline Samos, his betrothed, because he is uncertain about the future. He forces Mare to attend court with him as newbloods across Norta pledge their allegiance to him. One of the newbloods recognizes Nanny, a friend of Mare’s and member of the Scarlet Guard. Nanny comes forward and commits suicide in front of Maven. Upset, Mare destroys the books in her chamber and falls asleep. When she wakes up, she finds the books replaced by several more that belong to a friend, Julian Jacos.

Two princes from Piedmont, an ally nation, come to visit Maven. They question Mare before attending a royal dinner. During the dinner, several members of the royal Houses suddenly attack Maven. He escapes, but they kill one of the Piedmont princes before escaping. Although shaken, Maven takes Mare and goes on a coronation tour across Norta. They travel to the Lakelands, their enemy country, and Maven signs a treaty with their king. He agrees to marry the king’s daughter, Iris. While they travel, the Scarlet Guard attacks and successfully occupies Corvium. Cameron reunites with her brother.

Maven and Iris marry at Whitefire Palace, Maven’s home. During the ceremony, the sky goes dark and the Scarlet Guard attacks. Evangeline releases Mare in exchange for the safety of her brother, Ptolemus, and Mare reunites with Cal. She travels with the Guard to Piedmont, where she reunites with her family, Cameron, and Julian, as well as friends Farley and Kilorn. She learns that Farley is pregnant with Shade’s child. Farley gives birth soon after. Mare meets three other newbloods with her ability, called electricons. Meanwhile, Evangeline and her family travel to the Rift, and her father declares his rule over the region. They agree to help the Scarlet Guard protect Corvium and restore Cal as king of Norta. Mare and the Scarlet Guard fly to Corvium to fight off Maven’s army. They succeed with the help of the Rift, and their leaders meet. The Silvers offer to place Cal as the new king, but the Guard, and Mare, are opposed. Cal decides to become king despite their opposition.