This fantasy novel is set in an alternate 1889 Paris where a secretive organization called the Order of Babel safeguards Babel Fragments, ancient sources of Forging, a magical artistry that reshapes objects. Forging operates through two categories of affinity: mind (influencing memory, will, and illusion) and matter (influencing solids, liquids, or gases). The Order's French faction once comprised four Houses, but only House Nyx and House Kore remain. House Vanth's bloodline was declared dead, and the Fallen House was destroyed decades ago.
In the prologue, the matriarch of House Kore is attacked outside her home. An unseen assailant breaks her fingers, pries her Babel Ring—a Forged artifact central to her authority as matriarch—from her hand, and strikes her unconscious. The Ring is a critical artifact: It allows her to mark objects with her House's insignia and, together with the patriarch of House Nyx's Ring, guards the location of the West's Babel Fragment.
One week earlier, Séverin Montagnet-Alarie, the disinherited heir of House Vanth and owner of the luxurious L'Eden hotel, attends a masked Order auction to steal a Forged compass rumored to contain a treasure map. As a child, Séverin was stripped of his inheritance when the matriarch of House Kore and the patriarch of House Nyx administered a falsified test. Blackballed from auction houses, he became a thief who steals Forged antiquities for museums. His historian, Enrique Mercado-Lopez, a Filipino-Spanish scholar, hides inside a Forged statue with a decoy compass. When the swap nearly fails, Enrique discovers the mechanism's release phrase, and they escape with the real compass.
Séverin's team operates from L'Eden. Laila, a cabaret star known as L'Énigme, can read the history of any non-Forged object by touching it. Born stillborn in India, she was crafted into a living body by a
jaadugar, a Forging magician. She was told her body will not hold past her nineteenth birthday, and she searches for an ancient book stolen by the Order that may sustain her existence. Zofia Boguska, a young Polish-Jewish engineer with a Forging affinity for metals, was expelled from school after classmates bullied her, triggering an accidental fire. Séverin freed Zofia from prison and gave her a job. Tristan Maréchal, Séverin's sixteen-year-old foster brother and landscape artist, maintains L'Eden's elaborate gardens.
Séverin breaks open the compass to find a metal diagram bearing I Ching hexagrams, Chinese divination symbols, alongside four corner symbols that Enrique rearranges into the Eye of Horus. The group theorizes that looking through a Forged Horus Eye reveals a Babel Fragment's location, explaining why most Horus Eyes were destroyed during Napoleon's Egyptian campaign. Séverin sees this as leverage to reclaim his House.
Their plans shift when Hypnos, the young patriarch of House Nyx, sends Séverin a blood-Forged letter: "I know you stole from me" (59). The son of a French aristocrat and a woman descended from enslaved people in Martinique, Hypnos traced Séverin through blood left at the auction. He proposes a deal: Steal the Horus Eye from House Kore's vault, and he will administer a legitimate inheritance test. He explains that the matriarch's stolen Ring makes protecting the Fragment urgent and forces Séverin to swear an oath by threatening his friends with illusions of their capture.
Séverin returns to find everyone safe. All agree to help. First, Séverin and Tristan pose as a Sphinx, one of the Order's masked enforcers, and a police officer at the Palais des Rêves cabaret to obtain the Horus Eye's vault coordinates from the courier. When an extra Sphinx appears, Laila stages a dramatic distraction. Meanwhile, Enrique and Zofia break into the Exhibition on Colonial Superstitions to steal verit stone, a rare substance that neutralizes detection sensors. Inside, a man wearing a golden honeybee pendant ambushes them and speaks of revolution. They escape with the verit stone. Séverin privately discovers the courier has been murdered with a golden honeybee placed in his mouth.
The group infiltrates House Kore's Spring Festival at Château de la Lune under false identities. Enrique and Tristan create a diversion in the greenhouse while Laila hides inside a giant cake to access the matriarch's office and steal the vault key. She later performs onstage, concealing the key in her bangles and tossing it to Séverin. Séverin deduces that the real library lies underground beneath the greenhouse. After navigating a subterranean atrium protected by deadly traps, the group reunites in a vast underground library where hundreds of identical Horus Eyes serve as decoys. A massive Forged guardian called Ammit attacks when Laila accidentally triggers it, but she discovers its deactivation mechanism and neutralizes the creature. They secure the true Horus Eye.
In the greenhouse, Roux-Joubert, a sickly Fallen House member Séverin encountered at dinner, holds Tristan captive with a Phobus Helmet, a banned device that loops the wearer's worst nightmares. Roux-Joubert reveals he tracked the group through a homing device placed on Zofia and used the helmet to manipulate Tristan into betraying them. He seizes the Horus Eye and demands Hypnos's Babel Ring within three days.
Back at L'Eden, the group resolves to recover the Eye. Enrique connects the honeybee symbol to the Fallen House's hexagram, and Séverin concludes the Fallen House has risen. A relic bone clock projects images at midnight revealing the Fallen House meets in the catacombs of Paris, connected to the Exhibition through a hidden Tezcat door, an invisible portal crafted by the Fallen House. Séverin and Laila enter the catacombs while Zofia, Enrique, and Hypnos block the escape route with an impenetrable silver cloth.
Inside, they find Tristan still wearing the helmet alongside the Horus Eye and a Ring on a worktable. Laila reads the Ring and discovers it is fake. When Séverin lifts the helmet, it electrocutes him. Tristan, weeping, holds a knife to Laila but then forces the hilt into her hand so she can read what happened; she understands he was tortured and manipulated.
Roux-Joubert captures Séverin and demonstrates terrifying power: His blood runs gold, and by smearing it on Séverin, he forces wings and horns to sprout from Séverin's body. He reveals the Babel Fragment lies beneath the catacombs and begins awakening it, animating skeletons from the surrounding bones. He admits the doctor, the true leader of the Fallen House, who seeks to join the Fragments and achieve theurgy, the power to become gods.
Zofia, Enrique, and Hypnos join the fight. Hypnos pretends to surrender his Ring to buy time. While the doctor is distracted, Laila slams the Horus Eye into a depression in the floor, activating the Fragment's somno, a deactivation mechanism that puts it back to sleep. The doctor flees with the Fallen House's original Ring, and the Order's Sphinxes arrive, summoned by Hypnos's scattered jewelry.
A week later, the group celebrates, but Séverin learns Roux-Joubert has escaped. Roux-Joubert storms into the Palais des Rêves, setting fires and throwing a blade-brimmed hat. Séverin shields Laila, but Tristan is the true target. The blade slashes Tristan's throat, killing him.
Three weeks later, the matriarch and Hypnos arrive to administer the inheritance test, but Séverin refuses, consumed by guilt. Months of grief fracture the group. Laila discovers pinned, wingless birds hidden in Tristan's workshop, evidence of a darker internal struggle, and burns them to protect Séverin. She visits Séverin and kisses him, urging him to live. He cruelly pushes her away, dismissing her as less than real.
By November 1889, Séverin prepares for the Order's Winter Conclave in Russia. Laila forces a Forged oath onto his wrist, securing her place as his declared mistress to access leads on the ancient book she seeks. In the novel's final scene, the matriarch secretly visits Hypnos and reveals the original inheritance test was never falsified. Séverin is not the blood heir of House Vanth, and the matriarch insists he must never learn the truth.