The story starts with Alina Starkov and Malyev “Mal” Oretsev, two young orphans living in a Duke’s house in Karemzin. They are being tested by Grisha Examiners who aim to find out if they’re capable of using the Small Science, a system of magic-like abilities. The two orphans hold onto each other tightly, hoping not to be split up by the judgment of the Examiners.  

Years later, Alina and Mal are adults in the same regiment of the First Army of Ravka. The regiment has been tasked with crossing the Shadow Fold, an expanse of blackness that divides the country of Ravka in half. The Fold plays host to the volcra, monsters who feed on people and fear the light. During the crossing their sandskiff is attacked by volcra, resulting in numerous casualties. But when they attack Mal, magic is awakened inside Alina and light emanates from her. She scares the monsters away.  

When the skiff returns to the drydock, Alina is brought before the Darkling, a powerful Grisha who leads the Second Army. The Darkling tests her for power and finds that she is capable of manipulating light. Knowing that he has finally found the Sun Summoner, the only Grisha with the capability to affect the Fold, the Darkling sends Alina to the capital with a retinue of guards for protection. The Darkling tells her she may be able to destroy the Fold for good. Her carriage is attacked by Fjerdan assassins, and Alina only survives because the Darkling arrives just in time to save her.  

Upon her arrival at the Little Palace in Os Alta, the capital, Alina meets the King and Queen of Ravka and her presence brings hope to the war-torn country for the first time in many years. She befriends Genya, a Grisha woman who teaches Alina the ins-and-outs of Grisha life. Alina begins her training by researching Grisha history and theory, learning martial arts from a former mercenary named Botkin, and attempting to use her power with the help of an ancient Grisha woman named Baghra. At first, Alina is only able to use her power with the help of either the Darkling or Baghra, who act as amplifiers for other Grisha.   

Alina sends letters to Mal but receives no response for months. The lack of correspondence makes her feel alienated from Mal and she begins to believe that their relationship has crumbled. As a result, she realizes it was her love for Mal that made her hide her power since childhood. It’s only then that Alina can use her power without assistance. The Darkling and Baghra agree that she’s not powerful enough on her own to be able to manipulate the Fold, so the Darkling makes plans to find her an amplifier. He plans on making an amplifier from the horns of a legendary Morozovan stag which Baghra insists does not exist. One winter night, the Darkling surprises Alina by kissing her. 

The Darkling insists that Alina focus on honing her magic while he has his men search for the stag. On the night of the King’s winter fete, Alina participates in a demonstration of her power with the Darkling. Afterward, the Darkling and Alina escape to a secluded room and kiss passionately. Alina feels overwhelmed by the Darkling’s power, but she senses something strange about his actions. Soon, the Darkling leaves to follow up on a report about the stag. On her way back to her dormitory, Alina sees Mal walking through the hallway. Mal has been tracking the stag for the Darkling and has not received any of Alina’s letters. The two have a heated argument and part on bad terms.  

Alina is surprised later that night when Baghra arrives at her room and insists that she leave the capital. Baghra reveals that the Darkling is intending to use the stag’s antlers to control her power and expand the Fold instead of shrinking it. She also divulges that she is the Darkling’s mother and that the Darkling is the Black Heretic, the figure that created the Fold centuries ago. Convinced of the Darkling’s evil, Alina leaves Os Alta, hiding among performers departing the palace. She heads west and keeps herself as inconspicuous as possible. But Alina is forced to use her powers to defend herself which reveals who she is to nearby soldiers. Alina flees from the Darkling’s men into the forest, but they pursue her. Alina avoids them for some time before Mal rescues her and leads her to safety.  

When Alina reveals the Darkling’s plan to him, the pair formulates a plan to get to the stag before the Darkling, relying on Mal’s skills as a tracker. They search for the stag, travelling far north. Their journey is a hard one, punctuated by freezing temperatures, difficult terrain, and dangerous interactions with people on the road. One night Mal confesses his longtime feelings for Alina and they kiss. Then, Morozova’s herd wanders close to their camp. But rather than killing the stag, Alina chooses to spare its life. She is determined to find another way to defeat the Darkling. Just then, the Darkling’s men emerge from the woods in ambush. The Darkling takes the pair prisoner and kills the stag. He has the antlers permanently fastened around Alina’s neck and seizes control of her power.  

The Darkling takes Alina and Mal to the Shadow Fold, along with emissaries from the surrounding countries. Then he uses Alina’s powers to illuminate a wide path through the Fold, sending the volcra reeling away. The Darkling suddenly extends the Fold, which swallows up the village of Novokribirsk, as a demonstration of his power. He threatens to use the Fold as a weapon against any country that opposes him.  

As a final act of cruelty, the Darkling orders Mal to be thrown to the volcra. Horrified and furious, Alina tries to resist the Darkling’s power and keep Mal safe, but she’s unable to gain control. But as the darkness closes in on Mal, Alina has an epiphany. By showing the stag mercy and sparing its life, she has just as much power over the amplifier as the man who killed the stag. Alina suddenly regains control over her power and saves Mal. Though she tries to turn the other Grisha against the Darkling, none of them comply. She uses the powerful Grisha ability known as the Cut to first destroy the skiff’s masts and then to tear the entire skiff in half. Alina and Mal leave the Fold behind. They are unsure whether the Darkling has survived. They flee into the west and cross the True Sea to escape.