Queen of Air and Darkness

The third and final installment of The Dark Artifices trilogy, set in the Shadowhunter Chronicles universe of half-angel warriors called Nephilim, picks up after a catastrophic attack in the Council Hall of Alicante, the Shadowhunter capital. Annabel Blackthorn, an undead ancestor whom Julian Blackthorn brought before the Clave, the Shadowhunter governing body, has murdered both the Inquisitor Robert Lightwood and Julian's 15-year-old sister Livvy before escaping through a window bearing the broken-crown sigil of the Unseelie Court, one of Faerie's two rival royal courts. Emma Carstairs, Julian's parabatai (a warrior partner bound by an angelic rune), shattered the Mortal Sword, a truth-compelling blade, during the fight. Julian, who has secretly raised his younger siblings while concealing his forbidden love for Emma, is devastated. Parabatai who fall in love face a curse that grants destructive power before consuming them, and Julian, terrified, visits the warlock Magnus Bane, who casts a spell stripping away his capacity for love. The spell dampens all of Julian's emotions, leaving him cold and calculating.

In the political vacuum, Horace Dearborn, leader of a xenophobic faction called the Cohort, seizes the Inquisitor position. His daughter Zara and their allies consolidate power, pushing anti-Downworlder legislation targeting vampires, werewolves, warlocks, and faeries. Horace discovers Julian and Emma's forbidden love and blackmails them into a mission to Faerie: They must kill Annabel and retrieve the Black Volume of the Dead, a necromantic text. Unknown to Emma, Julian has made a photocopy of the Black Volume and plans to offer it to the Seelie Queen, ruler of Faerie's other royal court, manipulating their route without telling Emma.

The Blackthorn family scatters. Julian's older half-faerie sister Helen and her wife Aline take over the Los Angeles Institute, struggling to bond with the younger siblings, including seven-year-old Tavvy. Ty, Livvy's twin, reveals to Kit Herondale, a newly discovered Shadowhunter, that he intends to use necromancy to raise Livvy. Kit agrees despite misgivings. At the Scholomance, a Shadowhunter school, Diego Rocio Rosales, Cristina's former boyfriend, hides the faerie prince Kieran Kingson at the request of Cristina Mendoza Rosales, Emma's best friend. The Cohort discovers and tortures Kieran before he escapes with news that Horace sent Emma and Julian on a suicide mission. Cristina, Julian's half-faerie brother Mark, and Kieran travel to Faerie to rescue them, using the Eternidad, a family heirloom that opens passages between worlds.

In Faerie, Julian's emotionless state produces alarming behavior: He kills a Cohort assassin without hesitation. At the Seelie Court, the Queen accepts the copy of the Black Volume but privately tells Julian that breaking the parabatai curse would require destroying the original parabatai rune in the Silent City, the Shadowhunters' necropolis, using the now-shattered Mortal Sword. Mark's faerie aunt Nene warns them that the Queen plans to trade the Volume to the Unseelie King for her captive son Ash, fathered by the villain Sebastian Morgenstern. Emma and Julian join the Queen's procession to the Unseelie Tower.

Cristina, Mark, and Kieran are captured by Unseelie Prince Oban, but Cristina escapes and enlists Kieran's half-brother Adaon to help. Inside the Tower, Emma and Julian learn the King plans to use the Black Volume on Ash to create a weapon that destroys angelic magic, powered by a Portal to an alternate dimension called Thule. When the Seelie Queen confronts the King, Annabel seizes Ash and leaps through the Portal. In the ensuing battle, Adaon frees Jace Herondale and Clary Fairchild, allied Shadowhunters captured on their own Faerie mission, and Kieran kills the Unseelie King. Emma and Julian, cut off by fire, escape through the Portal into Thule.

Thule is a nightmare world where Sebastian won the Dark War, his earlier campaign against the Shadowhunters, and demons overrun the earth. Emma and Julian find a surviving version of Livvy, now a scarred rebel leader. Julian's emotions return because Magnus's spell cannot function in this magicless world. Tessa Gray, Thule's last surviving warlock, opens the sealed Silent City so they can retrieve the Mortal Sword and the Mortal Cup, the artifact used to create Shadowhunters, asking them to kill Sebastian in return. With help from Ash, who has aged years in Thule's accelerated timeline, Emma slays Sebastian. Julian kills Thule's Annabel to fulfill his vow and open her Portal home, then leaps through with Emma carrying the Mortal Sword. Before leaving, he carves a reminder into his arm that living without emotions is its own cage.

Back home, crises mount. Horace has declared Jace and Clary dead, blamed faeries, declared war, jailed Consul Jia Penhallow (the Clave's political leader), and passed a Downworlder Registry. Diana Wrayburn, the Blackthorns' tutor, escapes Idris after cutting off Horace's arm when he threatens to expose her identity as a transgender woman. Kieran and the Wild Hunt, a faerie cavalry host, retrieve water from Lake Lyn to cure a plague afflicting warlocks. Magnus removes Julian's spell, restoring his emotions but warning that their love will accelerate the parabatai curse. Emma discovers dark marks spreading on her skin and sneaks into the Silent City with the Mortal Sword, intending to destroy the original parabatai rune and sever every parabatai bond worldwide. Julian follows and stops her, urging her to wait one more day.

Julian assembles a resistance coalition of Shadowhunters and Downworlders called Livia's Watch, revealing Jace and Clary alive. Separately, Ty attempts his necromantic spell at Lake Lyn despite Kit's anguished plea, during which Kit declares his love for Ty. The spell partially works: Livvy appears as a ghost, warning Ty he has torn a hole in the fabric of life and death.

The resistance confronts Horace's staged parley with King Oban on the Imperishable Fields. Julian forces a Cohort leader to confess the conspiracy under the Mortal Sword, and full-scale battle erupts. Cristina kills Oban, and Kieran is proclaimed King of Unseelie. Dru, Julian's 13-year-old sister, frees jailed prisoners including Jia, who leads reinforcements to the battlefield after the Silent Brothers, mute Shadowhunter monks, blast open Alicante's gates. The Riders of Mannan, the Unseelie King's spectral horsemen, reveal that Kit descends from the First Heir of Faerie, making him heir to the High Kingship.

When Zara stabs Emma from behind, Julian reaches through their bond to save her, triggering the curse: They transform into towering Nephilim giants burning with heavenly fire. They destroy the Riders and kill Horace but grow increasingly uncontrollable. The Blackthorn siblings walk across the battlefield, each speaking to the giants about what Julian and Emma mean to the family. Tavvy's simple plea breaks through, and Emma and Julian collapse to human size, their parabatai runes burned away, the bond permanently severed.

Alec Lightwood, Jace's parabatai, is elected Consul. The Cohort holds the Council hostage by threatening mass suicide, and Alec agrees to evacuate Alicante rather than allow bloodshed. The Clave-in-exile establishes a new government in New York while Alicante becomes a self-imposed prison for the Cohort. Jem Carstairs, a former Silent Brother and Emma's distant relative, explains that the transformation was linked to the parabatai curse and that the bond is permanently broken. Free at last, Emma and Julian can finally be together openly. Kieran returns to Faerie as King but reunites with Mark and Cristina at Adaon's cottage, where all three can be together. Kit, learning his faerie heritage makes him a target, leaves without saying goodbye to Ty and goes to live with Tessa and Jem in Devon, England. Ty enrolls at the Scholomance, carrying the secret of Livvy's ghost. Magnus and Alec marry on the beach. In an epilogue, the Jace from Thule arrives at the Seelie Queen's court with a teenage Ash, demanding the Queen bring him Clary Fairchild.