A Torch Against the Night is the second book in the Ember in the Ashes series. Following up on the first book, it is told in alternating perspectives between the three main protagonists. Laia is a member of the Scholar class, which is generally enslaved by the powerful and evil Martial Empire. Elias is a former Mask (a powerful soldier who defends the Martial Empire), who has now joined forces with Laia in rebellion against the Empire. Helene is Elias’s former best friend and love interest who also attended the Mask military school with him and has since been named the Blood Shrike, a lead soldier who must swear allegiance to the Emperor, Marcus. The book traces Laia and Elias’s journey to rescue Laia’s brother Darin from the Kauf Prison, controlled by Martial forces. It also follows Helene as she is given the mission of finding and killing Elias to demonstrate her loyalty to the Empire.

The book begins with Elias and Laia fleeing through the streets of the city Serra, being chased by guards because Elias chose to save Laia’s life instead of continuing to compete to become the new Emperor. After a battle with the Commandment—the most powerful soldier in the Empire, who is also Elias’s mother—they escape to the desert and begin their journey toward Kauf Prison. However, Elias realizes that during the battle his mother cut him with a poisoned blade. He begins experiencing nightly seizures in which he travels to the Waiting Place, a spiritual realm controlled by a mysterious being known as the Soul Catcher. Meanwhile, back in Serra Helene is tortured by Empire soldiers for information about Elias and Laia’s escape.

Helene is released and given her mission by the Emperor, Marcus—she must find, torture, and kill Elias. She also learns that her sister, Hannah, is to marry Marcus. Laia and Elias travel to a dangerous desert outpost known as the Raider’s Roost to obtain an antidote to the poison. Laia finds the antidote at an apothecary, but then barely escapes a fight with a group of tradesmen, during which she makes her first kill.

During another seizure, Elias learns that he only has a few months to live and realizes that he had been exposed to nightweed, a deadly poison for which there is no cure. Helene is given three soldiers to aid in her search—two are her friends but the third is Harper, her former torturer and the Commandment’s spy.

Laia’s best friends, Izzi and Keenan, track her and Elias down in the desert and join them on their journey toward Kauf. This creates some tension as both Elias and Keenan have romantic feelings for Laia, and she has feelings for them both in return. The group travels through a sandstorm to the city of Nur, where various Tribes, groups of nomadic people, who Elias was raised by because the Commandment had abandoned him when he was a baby. Helene also tracks Laia and Elias to Nur.

Elias calls in a favor from a Tribal leader, Afya, to assist them on their rescue mission. Realizing that Helene and the Martial forces are in Nur, Elias’s adoptive family organizes a riot as a diversion so that Elias can escape the city. Helene is almost killed in the riot, but Elias saves her and she allows him to escape. While traveling through the desert, Elias has another dream about the Waiting Place and realizes that he must travel to Kauf on his own if he has any hope of arriving in time to rescue Darin before the poison kills him. He sets off by horse, but the Soul Catcher supernaturally transports him to the prison within days.

Helene is assigned a new task by Marcus—she must put down a rebellion by executing its leaders. She does so, winning Marcus new support from the terrified citizens. Laia, Izzi, Keenan, and the Tribal caravan are approached by a group of refugee Scholars who inform them that the Commandment is traveling throughout the land killing prisoners. Their wagons are then attacked by Martial forces; Laia is almost killed, but turns invisible and wages an attack against the Martial soldiers. Izzi is killed in the battle. Afya becomes angry at the sacrifices her Tribe is making to protect them, so Laia and Keenan continue on their own.

Elias breaks into Kauf, but he learns that Darin is dead and is then brutally interrogated for information. He befriends a Scholar child employed in the prison, named Tas. Helene visits the Augurs, who tell her that she is destined for greatness, but imply that she must kill Elias. Helene is visited by the Commandment’s cook, who is an ally of Elias and Laia. Cook informs Helene where Elias and Laia are going; in return, Helene uses her healing powers on Cook, who is suffering from a wound.

Laia and Keenan find shelter in a farmhouse that hides refugee Scholars, where they have sex. Meanwhile, Elias and Tas are tortured, but Elias learns that Darin is actually alive and trapped in a cell nearby. Helene, acting on Cook’s tip, arrives in Kauf, but the Warden refuses her entry.

Laia and Keenan arrive at Kauf Prison and set up camp in cave. Laia gives Keenan her silver armlet, but he suddenly transforms into the Nightbringer, an evil and powerful spirit who seeks possession of the armlet to free his kin, the jinn, who are trapped in the Waiting Place. Elias learns that the Warden is acting in concert with the Nightbringer.

Helene discovers the Commandment’s plan to overthrow Marcus and returns to Serra to warn him. However, he reveals that he was already aware of the plot, and publicly executes Helene’s family (except for her sister Livia, who offers to marry), as punishment for Helene publicly revealing the plot. Harper reveals that the Commandment had tasked him with killing Helene during their journey, but he now refuses to do so.

Afya shows up at Laia’s cave and offers to help her free Darin and Elias, saying she cannot go back on her promise. Elias makes a deal with the Soul Catcher that he will take her place if she gives him a bit more time to live and free Darin.

Laia, Elias, and Darin escape from the prison, along with thousands of other Scholars who break out with Afya’s assistance. One month later, Helene is still serving as Blood Shrike and plotting her revenge against Marcus, who now requests that she kill the Commandant. Elias returns to the Forest of Dusk to take on his new role as Soul Catcher. Laia lives at a cabin nearby and the two begin a romantic relationship. Darin wakes up from his coma.