Six of Crows follows a team of six talented young adults as they attempt a seemingly impossible prison break. The novel opens with a chapter from the perspective of a young Ketterdam guard who sees firsthand the power of jurda parem, a new, extremely addictive drug that increases the powers of Grisha; the guard is killed. On the other side of Ketterdam, Inej, Jesper, Kaz, and other Dregs successfully subdue a rival gang leader, though the group has obvious tensions. Kaz is kidnapped by Jan Van Eck, a rich man representing the Merchant Council. Van Eck offers Kaz 30 million kruge to break the man who invented jurda parem (Shu scientist Bo Yul-Bayur) out of Fjerda’s Ice Court. Kaz recruits Inej, Jesper, and Nina, who only agrees because Kaz shares that he also intends to break Matthias out of Hellgate prison. Nina is the reason Matthias is in prison, and even though their nations are enemies, she wants him to be free. The crew successfully infiltrates Hellgate, but as soon as Matthias sees Nina, he attacks her.
The crew subdues Matthias, and he agrees to join them when Kaz offers him a full pardon that would allow him to return to Fjerda. Kaz introduces the team to Wylan Van Eck, Jan Van Eck's son, then instructs them to gather supplies. Inej has a run-in with Heleen Van Houden, the woman who runs the Menagerie pleasure house, then finds that the crew’s ship has been bombed. She’s injured in the gang fight that follows, and Kaz saves her; the crew members flee to the real ship (the first was Kaz's decoy), kill their pursuers, and leave Ketterdam for Fjerda. On the trip, Nina uses her powers to heal Inej, and the crew learns that Kaz’s nemesis, Pekka Rollins, blew up the decoy ship. Rollins scammed Kaz in the past, and Kaz’s mission in life is to break Rollins’s gang empire down brick by brick.
The crew bonds and argues as they sail to Fjerda, and once they land, they cross frozen terrain to the capital, Djerholm. Nina and Matthias’s history is revealed on the way: Matthias was one of the drüskelle who captured Nina while she was recruiting for Ravka’s army, and they were shipwrecked. Trying to save his life, Nina got him wrongfully imprisoned in Hellgate. In the present, the crew comes across three pyres on which Fjerdans are burning Grisha alive, and Nina and Matthias are both horrified and angry at each other. They’re attacked by superpowered Shu Grisha on parem, and after the crew wins, Nina and Matthias agree that the two of them have to kill Bo Yul-Bayur and destroy parem, even if that means betraying the others.
The crew infiltrates the Ice Court, though there are some roadblocks and personal conflicts along the way, including Kaz finding Rollins in a prison cell, then returning to the crew covered in blood. Inej finds her true purpose (killing slavers like the ones who took her); Jesper reveals he’s a Fabrikator; Jesper and Wylan develop a flirtatious relationship; Nina is captured by Jarl Brum, who she thought died in the shipwreck over a year ago. Brum led the drüskelle that took her away from Ravka, and he shows her that Fjerda has been experimenting on Grisha for years. Matthias betrays Brum, his mentor, to save Nina—they discover that Bo Yul-Bayur is dead, but his son, Kuwei, is alive, so they decide to free him. The crew escapes in various dramatic ways: Kaz destroys Fjerda’s sacred ash tree; Inej steels Heleen’s precious diamond necklace; then Jesper, Wylan, and Inej commandeer a tank to break out of the Ice Court and drive the rest of the crew to safety at the harbor.
At the harbor, they’re met by Brum and an army of drüskelle. The crew agrees to die together rather than surrendering, but Nina chooses to take a single dose of parem instead; she overpowers the entire army, including Brum, and the crew escapes. Nina detoxes painfully as they sail home, and Matthias stays with her. Kaz asks Inej not to leave Ketterdam, but she doesn’t think a life with him (always on guard, never able to touch her) would be enough.
When they arrive in Ketterdam, they meet Jan Van Eck for the drop, though he double-crosses them. He never represented the Merchant Council—he wants jurda parem for his own profit. He orders Grisha on parem to kill them, but Kaz tries to dissuade him by revealing that Kuwei Yul-Bo is actually Wylan in disguise (the real Kuwei is at a secret location); Van Eck explains that he doesn’t care about his son, since Wylan can’t read and is therefore useless. Van Eck kidnaps Inej, now that he knows how much she means to Kaz, and leaves with the money. Out of resources and options, Kaz and the rest of the crew despair. Kaz promises to invent a new trick to get Inej and the money back.
The final chapter is from Pekka Rollins’s point of view, as Kaz and the others come to him for help. Kaz didn’t hurt Rollins back in the Ice Court, and now Rollins owes him a favor. Kaz trades his share in the Dregs empire for help and funds, and Rollins pities the young adults, until he realizes that they stole his watch, tie pin, and even shoe buckles. He decides that Kaz Brekker is a problem for another day; for now, there’s money to be made.
