Set in 1478 on the Italian peninsula, the story unfolds in a world where magic exists in an uneasy gray area: The Holy Roman Emperor tolerates it, while Pope Sixtus IV persecutes magic users, especially witches, through a brutal campaign known as the Veil of Fire. The Republic of Florence is ruled in all but name by the Medici family and their mysterious allies, the Luni
famiglia, an immortal family of unknown origin.
A prologue set ten years earlier establishes the central trauma of Ravenna Maffei's life. At thirteen, while visiting an alabaster quarry with her aunt, a renowned sculptress, Ravenna is startled by a stranger in the tunnels. An eruption of blue light from her body wraps around the man, rapidly aging him until only bones remain. Ravenna discovers she carries a lethal power she views as evil and spends the next decade suppressing it.
By 1478, Ravenna is a sculptor and the eldest daughter of innkeepers in Volterra, a city under Medici occupation. Her younger brother, Antonio, has been imprisoned in a cage in the public square for resisting the occupation. When the Luni
famiglia announces a sculpting competition with a boon as the prize, Ravenna enters despite her parents' fear that she will expose her magical heritage. She completes a marble Pluto, god of the underworld, embedding a Nightflame, a rare magical gemstone inherited from a distant witch ancestor, into its chest.
Cavaliere Saturnino, the eldest Luni son and heir to a dukedom, declares Ravenna the winner. She claims Antonio's release, but Signor Silvio Luni, the patriarch, announces Ravenna will accompany them to Florence as their artist in residence. Guards force her into a carriage. During an overnight stop, Saturnino intercepts her escape attempt. When her dark magic involuntarily strikes him, it has no effect, hinting at his inhuman nature. He kills a guard who fell asleep on duty, demonstrating the lethal stakes within his household.
In Florence, the Luni family leads Ravenna into the palazzo's dungeon, where five massive blocks of enchanted stone from the fae lands, a magical otherworldly realm, each protect a Nightflame at their center. Signor Luni demands she extract all five by the tenth of May, twenty-nine days away. Previous sculptors hired for the same task were killed by the stones' volatile magic or by the family. Ravenna refuses to work unless the family arranges a meeting with Lorenzo de' Medici so she can negotiate relief for Volterra. The family reluctantly agrees and assigns Saturnino as her permanent guardian.
At the Palazzo della Signoria, Florence's seat of government, Ravenna asks Lorenzo to cease arrests, restore confiscated property, and lift the curfew in Volterra. Lorenzo agrees to consider the request. Separately, the pope's courier, a wizard carrying a staff embedded with magical gemstones, delivers a letter demanding Ravenna sabotage the Luni family's plans and serve as his spy. If she refuses, the pope threatens excommunication of her, her family, and all of Volterra. The courier tells her to think of the stone as alive, protecting its charge with motive and reason. Ravenna reluctantly agrees.
Saturnino catches Ravenna returning and deduces the pope's involvement. They strike a bargain: Ravenna will share enough information to be useful without endangering her family, and Saturnino will protect her if her dual role is discovered. Saturnino challenges Ravenna's shame about her power, arguing it is a gift, and coaxes her to let her magic flow freely. When she does, midnight-blue light envelops the stone and subdues its defenses, allowing her to chip away a sizable chunk.
Complications multiply. Ravenna's maid, Imelda, and Imelda's brother Pietro are revealed as the pope's operatives inside the palazzo, threatening Ravenna when she fails to produce results quickly enough. The pope orders Ravenna to lure Galeazzo Sforza, Duke of Milan, to Ponte Vecchio at midnight during a banquet. She complies and watches Sforza assassinated by crossbow. Among the assassins is Antonio, now a priest in the pope's service. Saturnino arrives, is shot, and falls into the Arno. Ravenna dives in and discovers he cannot swim because his body is part marble. She pushes him along the riverbed, surfacing repeatedly for air, until they reach the bank.
In his hidden tower apartment, Saturnino reveals the full truth. He and his family were once marble statues carved by a fae sculptor from celestial stone, a magical material from the heavens. A witch named Simonetta, the pope's former mistress, stole the statues and used Nightflames to bring them to life nearly a century ago. The Nightflame in each of their chests is burning out; on the tenth of May, they will revert to stone unless the gemstones are replaced and the spell recast by a witch. Their purpose is to protect Simonetta's illegitimate son: Lorenzo de' Medici, whose biological father is the pope.
This revelation transforms Ravenna's relationship with her power. She stops viewing her magic as sinful and, working with calm purpose, extracts the first Nightflame. Imelda and Pietro attack her in the dungeon. Saturnino intervenes, banishing Imelda and killing Pietro in self-defense. Fortuna, the youngest Luni sibling, separately poisons Imelda before she can escape the palazzo.
Saturnino insists Ravenna leave for her safety. They exchange private marriage vows, and he provides legal documentation making her his heir. Rather than flee, Ravenna tracks down Antonio and begs him to leave Florence. He refuses, insisting the pope's mission is holy.
On Easter Sunday, Antonio and two other priests attack the Medici brothers during Mass at the Florence cathedral. Giuliano de' Medici is stabbed to death; Lorenzo survives. The mob seizes and kills Antonio. Ravenna witnesses her brother's death before Saturnino carries her to safety.
Ravenna, Saturnino, and the courier devise a plan: Florence will invite the pope to a jousting tournament on the tenth of May. The pope will attend expecting to reclaim his statues; instead, Ravenna will assassinate him using an enchanted mallet designed to destroy the pope's chain mail, a garment of fae-forged iron that extends his life. Ravenna extracts the remaining four Nightflames, and the Luni family agrees to the plan.
On tournament day, Marco, Saturnino's younger brother, betrays the family by delivering Ravenna directly to the pope in exchange for being the sole family member restored to human form. Ravenna shatters the pope's chain mail, but the pope reveals her family in chains, a hidden army, and a stolen war machine designed by Leonardo da Vinci and powered by the Nightflame from Ravenna's original statue. The machine spews fire across the piazza. At sunset, the Luni family turns to stone. The pope orders Ravenna burned at the stake.
As flames rise around her, the black cat Ombretta, Ravenna's constant companion, races to the pyre and transforms into a golden-haired woman: Simonetta, the witch who created the Luni family. The fae king punished her a century ago by turning her into a cat for stealing the Nightflames. Simonetta confronts the pope and uses an amulet to transform him into a snake. The courier freezes the war machine. Moved by Saturnino's kindness to her when she was a cat, Simonetta agrees to recast the spell. Using a Nightflame Ravenna retrieves, she restores Saturnino to life. He awakens fully human, warm-skinned, and weeping for the first time.
An epilogue set one year later shows Ravenna and Saturnino living in the palazzo, married, with Ravenna running a sculpting studio and expecting their first child. The remaining Luni family members stand as statues in the garden. Simonetta, still shifting between cat and human form, has discovered the four Nightflames Marco hid before turning to stone, leaving open the possibility of the others' restoration.