King of Ravka Nikolai Lantsov attempts to rebuild his country after the Ravkan Civil War and get it in order to fend off threats from neighboring nations Shu Han and Fjerda while dealing with the demons the Darkling infested him with. Zoya Nazyalensky, his friend, a powerful Squaller, and general of Ravka's Second Army, is desperate to help him.
They also run into the Cult of the Starless Saint, who worship and claim loyalty to the Darkling. Yuri, the leader of this cult, travels with Zoya and Nikolai while they are searching for a way to control the monster inside of Nikolai. They are trapped in a remnant of the Shadow Fold that holds some of Ravka's Saints, including Sankta Elisaveta, Sankt Juris, and Sankt Grigori. Sankta Elisaveta helps Nikolai prepare for a dangerous ritual to rid himself of the monster, while Sankt Juris works with Zoya to hone her Grisha powers. Elisaveta ends up betraying Zoya and Nikolai with Yuri's help. Juris is murdered by Elisaveta and is joined with Zoya as an amplifier. By the end of the ritual, the Darkling's spirit has entered Yuri's body.
Meanwhile, Nina Zenik is disguised as a woman named Mila Jandersdat as she, Leoni, and Adrik help Grisha flee Fjerda, where Grisha are oppressed and even hunted. Shortly after burying her lover, Matthias, Nina meets Hanne, a Grisha living in secret in Fjerda. Hanne is revealed to be the child of Jarl Brum and Ylva, a Hedjut woman. Together, Nina and her allies manage to rescue young Grisha women and children who are being drugged with parem and forced to conceive children born already addicted to the drug.
In the second half of the novel, Isaak, a member of Ravka's royal guard, is introduced. He is recruited by the Grisha at the palace to impersonate Nikolai, who has gone missing while on a mission to rid himself of the monster. Isaak struggles to hold his facade as the King of Ravka while attempting to find Nikolai a politically advantageous bride, finding interest in Princess Ehri of Shu Han. However, Princess Ehri is revealed to actually be a member of the Shu Han secret guard and fatally stabs Isaak and then herself, planning to frame Fjerda for the murders. The real Princess Ehri was disguised as a member of the secret guard. Despite witnessing this, Nikolai chooses the real Princess Ehri to be his bride.
