The following version of this book was used to create the guide: Schwab, V.E. A Conjuring of Light. Macmillan Publishing Group, 2017.

Schwab's novel is split into 15 parts, with seven to ten chapters in each. The entirety of the novel takes place over a few days. Lila, a thief-turned-magician from Grey London, is the initial lens into the novel. There are four main protagonists in A Conjuring of Light: Lila as previously mentioned, the crown prince of Red London Rhy, his adopted brother Kell, and the pirate Alucard. The main villain is the shadow king Osaron, with the White London magician Holland playing both the role of villain and hero. The main characters are all in their early-to-mid-twenties. The novel is told from multiple third-person perspectives, ranging from the main characters to smaller players who only get a few chapters, such as nine-year-old Nasi. The driving force of the novel is the four protagonists quest to defeat Osaron, who tries to take over Red London.

Schwab starts her novel from the perspective of Lila, with the action picking up right where the prequel A Gathering of Shadows left off. The beginning of the novel moves settings frequently between White London and Red London. Osaron tortures Kell and possesses Holland in White London while Lila works on a way to rescue Kell. Kell, desperate to save his dying adopted brother Rhy, tries to break out. However, he is too late and Rhy dies in the arms of his boyfriend Alucard in Red London. Lila arrives in White London using her Antari magic and frees Kell after killing one of Osaron's subjects, Ojka. The two travel back to Red London where Rhy comes back from death due to his magical bond with Kell. So long as Kell is alive, Rhy cannot truly die.

While Rhy recovers, still comatose, Kell explains what happened in White London and the threat that Osaron poses to his adopted parents King Maxim and Queen Emira. Meanwhile, Osaron crosses over from White London and begins his attack on Red London. He targets the Tassen Easch winner's ball, a celebration of the end of a magical competition. Osaron attacks the ball, and Kell comes running to fend him off. Despite Kell's Antari magic, Osaron is able to overpower him and Lila. He leaves Holland's body and dives into the red River Isle, turning it black. He begins to possess people all across the city to do his bidding or perish. Lila and Kell do their best to protect the people using their Antari blood.

King Maxim allows Osaron to take over the city in order to ensure that no more lives are lost, a move that surprises Kell. Kell visits Holland in the dungeon and presses him to divulge Osaron's weaknesses. Once Alucard realizes what is happening to the city, he leaves Rhy's side and runs off to find his siblings. Queen Emira sits vigil by Rhy's instead and is overjoyed when he awakes. Alucard finds his sister Anisa is possessed by Osaron and tries to save her.

Back in White London, a young girl named Nasi is the only one who mourns Ojka's passing. In Red London, Holland has nightmares in the dungeon; through these nightmares the reader learns that Holland's older brother Alox tried to kill him when he was nine. King Maxim and Kell plan their defenses against Osaron with the noble council. The head magician Tieren realizes that the blood sigils that Lila and Kell made on people are fading. Rhy interrupts and joins the council, who all decide that Kell should lure Osaron into a fight.

The city descends into chaos and Alucard manages to overcome Osaron's possession because he denies him permission. Rhy looks for survivors in the city. Holland and Kell talk in the dungeons, and Holland explains that Osaron needs an Antari body to truly rule Red London. Holland, as the only other Antari besides Kell and Lila, offers himself as a sacrifice to Kell, saying that his death would mean something. In a flashback, the reader sees that Holland's first love Talya tried to murder him in exchange for money when he was 18. Kell and the king agree that Holland should be used as bait, as he requested.

In Grey London, a magician named Ned Tuttle hears Osaron's voice and works to block him. Meanwhile, Kell confronts Osaron head on at the Red London palace. In the chaos, Osaron pushes Holland into the river and Kell dives after him. Kell manages to save Holland but just as he is about to resurface, Osaron grabs him. Kell realizes this was all a trap to get to him. When Lila does not see Kell resurface, she dives in after him. Holland and Lila work to get Kell free. Angry that his plan failed, Osaron sulks and builds a black palace on the river as his new home.

Lila, Kell, Alucard, and Holland continue to plot a way to defeat Osaron. The head magician Tieren suggests that they use an Inheritor to capture Osaron and make sure his magic does not escape. Alucard says he knows of one they can buy at the floating black market called Ferase Stras. The foursome heads to the black market while Rhy stays behind to protect the city. They sail on the ship the Ghost with the help of a pirate named Jasta. At the black market, Lila buys the Inheritor from Maris Patrol using three years of her life. She also receives a new eye in exchange for a favor. Alucard and Kell buy a mirror and an Antari binding ring respectively. On their way back, they are attacked by Sea Serpent pirates and realize that Jasta betrayed them. The foursome manages to make it back to Red London after only four days away, only to discover that assassins from a rival kingdom killed Queen Emira, nearly killed Rhy, and that King Maxim sacrificed himself to Osaron to protect his people.

The final battle approaches and Osaron brings Ojka's body from White London and possesses it. He goes after the new king, Rhy, and tortures him in his black palace on the river. Lila, Kell, and Holland use the Antari binding ring to combine and share their power, allowing them to gain the upper hand over Osaron. Holland grabs the Inheritor and activates it, defeating Osaron and sacrificing his own powers in the process. The battle is won.

In the aftermath, Holland asks to be taken to White London, where he dies peacefully. Kell and Lila ask Ned Tuttle in Grey London to bury the Inheritor to keep it safe before sailing away on the Night Spire. Alucard, having given the Night Spire to Lila, stays with Rhy. The two lovers make up after Alucard uses the mirror he bought at the black market to show Rhy that his love for him is true. They wave goodbye to Kell and Lila as they sail off.