|Cover artist||Cliff Nielsen|
|Release Date||March 19, 2013|
|Publisher||Margaret K. McElderry Books|
| Preceded by|
| Followed by|
City of Bones
| Released after|
City of Lost Souls
| Released before|
City of Heavenly Fire
Tessa Gray should be happy—aren't all brides happy? Yet as she prepares for her wedding, a net of shadows begin to tighten around the Shadowhunters of the London Institute. A new demon appears, one linked by blood and secrecy to Mortmain, the man who plans to use his army of pitiless automatons, the Infernal Devices, to destroy the Shadowhunters. Mortmain needs only one last item to complete his plan.
He needs Tessa.
Charlotte Branwell, head of the Institute, is desperate to find Mortmain before he strikes. And Jem and Will, the boys who lay equal claim to Tessa's heart, will do anything to save her. For though Tessa and Jem are engaged, Will is still in love with her.
The last words of a dying Shadowhunter provide the clue that might lead Tessa and her friends to Mortmain. But their small group cannot stand alone, and the powerful Consul doubts that Mortmain is coming. Deserted by allies, the Shadowhunters find themselves trapped when Mortmain seizes the medicine that keeps Jem alive. With his best friend at death's door, Will must risk everything to save the girl they both love.
To buy Will time, the warlock Magnus Bane joins with Henry Branwell to create a device that could help defeat Mortmain. As they all work to save Tessa and the future of the Shadowhunters that resides with her, Tessa realizes that the only person who can save her is herself—for in the discovery of her own nature, Tessa could become more powerful than she ever dreamed possible. But can a lone girl, even one who can command the power of angels, face down an entire army?
Danger and betrayal, secrets and enchantment, and the tangled threads of love and loss intertwine as the Shadowhunters are pushed to the very brink of destruction in the breathtaking conclusion of The Infernal Devices trilogy.
In York in 1847, Aloysius Starkweather's granddaughter "Adele" is set to receive her first Mark, the Strength rune, because of her fragility and delicacy. Adele fearfully and reluctantly lets the Silent Brothers perform the ritual, soothed by her beloved grandfather. However, Adele cries out in agony, and it is too late when they realize that she cannot handle the rune.
In London in 1873, Charlotte Branwell interrupts a young Will's target practice in the training room to introduce to him the new ward, Jem. Will, as usual, is rude to the boy and calls him sickly, as if "doddering to the grave," much to Charlotte's disappointment. However, Jem is seemingly unaffected by his words and points out to Will that he is indeed dying. Will apologizes and expresses concern. Jem tells him not to feel sorry for him. Jem tells him that he is a good shot and can help improve his skills. Much to Charlotte's surprise, Will agrees to train with him.
Back to the present, London in 1878, Tessa is trying out her gold wedding gown when Jem knocks on the door. The superstitious and pregnant Charlotte insists that Tessa hide so Jem does not see her in her wedding dress, as it is bad luck among Shadowhunters. Jem tells them that Gabriel Lightwood was in the Institute, "making the most dreadful row."
In the training room, Will is training his sister Cecily. Even two months after her arrival, Will is still seemingly not pleased that she is there, while Cecily has already adjusted, though is still trying to get Will to write to their family. Cecily has practiced knife-throwing in secret, so she confidently bet Will that he must write to them if she hits the target thrice; she does, though Will twists her words by saying that while he will write them, he did not agree to send it. Before the two can argue any further, Jem interrupts them and tells them that Gabriel is making a scene downstairs.
Elsewhere, Sophie is bringing Gideon scones he asked for, along with some food Bridget prepared for him. He tries to talk to her, but Sophie is determined to avoid him, telling herself that her feelings for him will get them nowhere as she is a mundane servant, and that she has everything to lose, while Gideon does not. Gideon is just about to ask Sophie something before Henry arrives to tell Gideon about Gabriel.
With everyone gathered at the entrance of the Institute, Gabriel, upon seeing Gideon, finally tells them his problem: their father, Benedict, has turned into a demon, in the form of a worm. Will, Jem, Gabriel, Gideon, Henry, Cecily and Tessa then go over to the Lightwood's country home in Chiswick, and Gabriel kills Benedict with an arrow through the eye. Gabriel truly opens his eyes to Cecily that night - she jumps onto Benedict, distracting him despite minimal training. Gabriel cuts off Will's scolding, saying 'That was one of the bravest things I've seen a Shadowhunter do.'
Meanwhile, unbeknown to the residents of the Institute, there is an issue of who is going to become the next Consul. While the members of The Council suggest Charlotte, Consul Wayland disagrees due to not wanting to lose his own legacy, and suggests his nephew George Penhallow instead.
Will discovers the next day that Jem has been taking extra doses of yin fen, a process that would accelerate his death. Jem explains it's because he told Tessa his love for her was making him stronger, and he feared Tessa would think his love for her was lessening. That day, Jem also allows Will and the others to continue the search for a cure, something he'd forbidden them to do a few years ago.
At about midnight, a distraught Will tells Tessa that someone has bought up all the yin fen - he'd spent that entire evening visiting suppliers, but they were all out of stock. They seek out Magnus for help, but come back empty-handed - save for a pendant that warns when demons are close.
Consul Wayland, upon hearing that Benedict (as a demon) has been slain by Gabriel, lures he and Gideon away for a 'private talk.' He blackmails them into agreeing to expose Charlotte's correspondence - hoping to manipulate the information into something to use against Charlotte. Gabriel and Gideon decide to write irrelevant letters to the Consul, hoping he will give up on them and leave them alone.
Mortmain sends a letter to the Institute confirming that he has bought up all the available yin fen. He asks for Tessa in exchange for the drugs. Jem refuses to allow Tessa to give herself up.
That night, Jem and Tessa decide they will marry the next day instead of their scheduled wedding in December.
Jessamine is brought back to the Institute the next day - the scheduled date of Jem and Tessa's wedding. The Magister's automatons attack with Mrs. Black and kidnap Tessa. Jessamine, having taken a fatal stab to the back, drags herself over to Will to tell him that Mortmain is in 'Idris', commenting that he is a terrible Welshman, before dying.
Cecily overhears Will's conversation with Jessamine before she dies and later figures out (by using Jessamine's last words as a clue), that Mortmain is hiding in Cadair Idris, a mountain near where Will used to live in Wales. She asks Gabriel to fetch Will from Jem's side, and she tells him where she believes Mortmain is hiding.
The Consul visits the Institute after the attack and talks to Charlotte. He refuses to send anyone after Tessa, as she is not Nephilim. Before he leaves he talks to Gabriel in private, and convinces him to spy on Charlotte, but without Gideon's knowledge, to save his family honor.
Will asks Magnus Bane to help them find a cure for Jem, who is dying and running out of yin fen. Magnus asks Will if Jem knows that he is in love with Tessa (believing Jem to be unconscious), but Will tells Magnus that he did not want to hurt Jem. Jem (who turns out to be awake) overhears and gives Will his blessing to rescue Tessa, and leave him to die.
Will goes to the stables to saddle Balios, and is found by Cecily. They have a talk, and Will promises that, if he survives and returns, he will visit his parents and tell them the truth about the curse. He gives her the demon-detecting pendant Magnus gave him, and leaves.
On the way to Mortmain's lair Mrs. Black reveals to Tessa that Mortmain resurrected her to serve him again, and has promised her an automaton body if she succeeds. Tessa tries to escape by jumping out of the carriage into a ravine. She is saved by her clockwork angel, but caught again by Mrs. Black.
Back at the Institute Will is found missing, and Charlotte forces Cecily to explain what happened. She admits he has gone after Tessa, and Charlotte takes charge, giving out tasks to the Enclave and sending a message to the Consul. Magnus, still at the Institute, is sent to help Henry with his work. Together they begin working on Henry's latest invention: the Portal, which can teleport a person from one place to another.
On the road to Wales, Will feels his parabatai rune bleeding, as well as blinding pain, and realizes that Jem has died. He throws up and asks Woolsey Scott, who he meets at a roadside inn, for advice after he gets into a fight with some of his werewolf pack. Will cuts his hand with Jem's dagger, buries it in the ground by a tree and vows to find it once again.
Tessa wakes up in a cave in Cadair Idris. She is trapped by an invisible barrier, and Mortmain appears to speak with her. He tells her the story of her birth, and explains that her clockwork angel was meant to be a gift from his father to his mother, to protect her, though he never finished it. Mortmain reveals it contains a bit of an angel's soul, and that he finished it, tuned it to her life, and gave it to her mother to keep her safe in the womb. He tells her he intends to use her to breed a new race of half-demonic Shadowhunters.
He convinces Tessa to Change into his father in exchange for yin fen sent to Jem. She does as he asks, and Mortmain gets a formula from his father, one that will allow him to bind demon energies to his automatons. Tessa tries to undo the Change but is too late to stop John Shade from writing down the formula. Mortmain sends her back to the room, and finishes binding demons to his machines.
At the Institute Charlotte receives a letter from the Consul, who refuses to send reinforcements based on Will's discovery of Tessa's jade pendant on the road to Wales. As she finishes reading the letter Sophie announces a man to see her. Aloysius Starkweather enters the room, surprising Charlotte, and tells her that he has discovered what happened to his granddaughter. He explains that he recently interrogated a faerie, who filled in the blanks for him. Due to his family's practice of taking spoils after the Accords, the faerie community decided to take revenge by switching his newborn granddaughter for a sickly mundane. The mundane died after being Marked, and the real Adele was raised as a mundane, unmarked and unaware of her heritage.
Aloysius reveals that the faerie also told him what happened to Adele; she married a mundane, Richard Gray, and had a daughter, Tessa. Charlotte is skeptical, but realises that since Adele was unmarked, it is possible that Tessa could have been born. Aloysisu believes that Mortmain learned of Adele, and loosed an Eidolon demon on her to create someone like Tessa; half-demon and half-Shadowhunter. He tells Charlotte he doesn't trust Tessa with the Council, and knows Charlotte she will do everything to help Tessa. Before he leaves he tells Charlotte to let Tessa know that she is welcome to the name of Starkweather. Charlotte sends a letter to the Consul, including all this new information but leaving out Aloysius' name, as she knows the Consul won't trust him.
Gabriel overhears this and writes a letter to the Consul discrediting Charlotte. Sophie tells him Charlotte needs to speak with him. Gabriel worries she knows what he is doing, but Charlotte just wants to ask if he's okay, and dealing with the guilt of killing his father. Gabriel breaks down and Charlotte holds him while he sobs into her shoulder. He realises the Consul is wrong about Charlotte.
Later, Charlotte receives another letter from the Consul telling her to stop pushing for an attack on Cadair Idris. She is hurt, and can't understand why he is so rude to her. Gabriel tells her that the Consul will never listen to her, and reveals that he asked him to spy on her, though he never sent the letter he wrote. Gideon and Sophie speak up as well, and Charlotte realises the Consul just wants her to be removed as head of the Institute, because he can't control her. Gabriel thinks to himself that the real reason the Consul wants Charlotte gone is because she inspires loyalty like he never could. Charlotte resolves to send a letter to entire Clave asking for reniforcements, though she knows the Consul will remove her position for going over his head.
Everyone agrees to fight with Charlotte, even the servants, and when she questions their ability to defend themselves, Gideon speaks up for Sophie, saying that she has natural talent and would make a fine Shadowhunter someday. He unwittingly blurts out that he intends to marry her, shocking her. Cecily clears the room and her and Gabriel listen outside as Gabriel declares his love for Sophie and asks her to marry him, which she happily agrees to. Bridget starts singing one of her songs, and Sophie excuses herself to go strangle her.
Tessa is awoken by Mortmain to show her his new automatons, animated by demon energy. He demonstrates the ineffectiveness of runed weapons on them. Tessa tries to appeal to his better nature, and Mortmain punishes her by forcing her to watch the automatons destroy a small Welsh village outside the mountain. Will, who had been sleeping in one of inns, is caught in the demonstration but manages to escape on Balios. He follows the automatons back into the mountain. Tessa, in her despair, tries to destroy the clockwork angel so she may die and prevent Mortmain from using her. She smashes it with a fireplace poker, but the poker shatters and an angel appears before her. It asks her why she wants to destroy her safety. She apologizes to it for being trapped so long, but the angel tells her it doesn't blame her. Tessa asks it to let her die, but the angel sadly tells her that it cannot, and disappears. Before it leaves, Tessa asks its name, and the angel tells her: Ithuriel.
Will eventually finds Tessa in Mortmain's hideout, and rushes to her without thinking, causing him to be trapped inside the invisible barrier with Tessa. Believing that Jem is dead and thinking that they will both die, Will confesses everything to Tessa and tells her how much he loves her, then they both have sexual intercourse during the night.
The next morning, Tessa wakes up and realizes that her clockwork angel is on Will's shoulder near his neck, and she pulls it away to find that it has left a mark in the shape of a small white star, thus creating the mark of the Herondales that will be seen on the descendants in the future generations.
The Enclave members are disappointed when only a few Silent Brothers (Brother Enoch, Micah and Zachariah) arrive to help, though Brother Enoch explains that the only reason more haven't come is because Consul Wayland called a mandatory Council meeting. The Shadowhunters use the perfected Portal to travel to Cadair Idris.
At the Council meeting Consul Wayland asks for a replacement for the head of the London Institute, which causes dissent as many people have received her letter and question wether the information is true. Charlotte's aunt Callida and the Inquisitor diagree with his decision to ignore her request for help, and Aloysius Starkweather openly speaks out against the Consul. The Inquisitor is disgusted at the Consul's disliking of Charlotte due to her gender, and begins arguing with him. The Council is suddenly attacked by a portion of Mortmain's automaton army, and the Consul is beheaded before he can reveal why he hates Charlotte so much. Aloysius chuckles to himself, saying that Charlotte warned them what would happen, before his throat is crushed by the same automaton that killed the Consul. The Shadowhunters begin fighting, but their weapons are useless against the demonically enhanced machines.
Meanwhile, Magnus Bane finds Will and Tessa and gives a comment regarding what they were doing. Relieved and embarrassed, Will quickly puts on his clothes along with Tessa, and they both follow Magnus to where the others are. The others are fighting hundreds of automatons, and they are losing.
Will joins in the battle right away, telling Magnus to keep a watch on Tessa. However, in the middle of the battle, Will finds out that one of the Silent Brothers, Brother Zachariah, is actually Jem. At the same time, Tessa gets kidnapped again and Mortmain holds her, threatening Will and the other Shadowhunters with her. Tessa Changes into the angel trapped inside her clockwork angel, Ithuriel, leaving Will in awe as he watches her blaze with fire. The angel protects her as she transforms, and she kills Mortmain, but the heavenly fire of the angel overwhelms her and she Changes back, losing consciousness. Ithuriel's soul escapes.
Tessa is taken back to the Institute infirmary and spends a long time unconscious. The Silent Brothers even try runes on her, but they simply fade away. Will is sick with worry, and begs Charlotte to summon Jem so he can help Tessa heal. Gabriel finds Cecily by the stables and they have a conversation, which ends with them kissing. The Inquisitor visits the Institute and hands Charlotte a letter from the Council, asking her to be the next Consul. She asks for time to think, and is later convinced by Sophie to accept on the condition that she runs the Council from the Institute for the first few years, that Will becomes the next head of the Institute, and that Jem is summoned from the Silent City to end his engagement to Tessa. The Council accepts and summons Jem.
Tessa speaks with Jem, and after a long conversation they decide that every January they will meet for an hour on Blackfriars Bridge. Tessa says goodbye to him, and she recovers soon after. Will also has a conversation with Jem and says goodbye, and is sad for weeks after he leaves, but he eventually goes back to his old self.
Sophie succesfully Ascends and becomes a Shadowhunter. The annual Christmas party of the Shadowhunters happens the same day at the London Institute and Jem's uncle, Elias, arrives to give Will a sword, Cortana. Will refuses, after being reminded of his memories of Jem, and escapes outside to sit on the stairs in front of the Institute. Jessamine visits him (in ghost form) and tells him to propose to Tessa as she sees that he loves her very much. Tessa tells Elias to give the sword to his children.
Later on, when Tessa comes out to talk to Will he proposes to her and she says yes. They schedule to marry when Will turns 18, and he uses Henry's Portal to go back to Wales along with Cecily, Tessa, and Gabriel to visit his parents. Will and Cecily have a happy reunion with their parents, and Will announces that Tessa is his fiancee.
Tessa and Will get married and have two children, James and Lucie. It is revealed that Will dies of old age at 78 years old in 1937, and Jem, as Brother Zachariah, visits him on his deathbed and plays to him on his violin for one last time. Tessa is heartbroken when Will dies and begins to travel with Magnus Bane, who understands the grief of outliving loved ones. The two part ways in New York where they went because of World War II. Church the cat comes with them and is dropped off at the New York Institute.
Later, in 2008, Tessa is meeting Jem on Blackfriars Bridge when she sees that Jem is no longer a Silent Brother or dependent on yin fen. They reunite and kiss; Tessa invites Jem to travel the world with her. Tessa also recalls the pain of watching Will die and leaving her family when she realizes how her children, and grandchildren will age while she remains young. She vows to not get close to her descendants as she doesn't want to cause or bear any pain.
- The first edition copies of Clockwork Princess came with the genealogical tree of the Carstairs, Herondale, and Lightwood families, thus linking the London Shadowhunters of The Infernal Devices to the Shadowhunters in modern day New York and Los Angeles.
- The original (now hardbound) cover features Tessa Gray holding the Shadowhunter's Codex and wearing the clockwork angel pendant against a backdrop of the Blackfriars Bridge. The repackaged (paperback) cover also features Tessa, this time sitting on the ground, wearing a bloody dress. Her necklace, the one holding her clockwork angel pendant, is on the ground in front of her, while a bigger illustration of the clockwork angel stands behind her.
- The cover model for Tessa on the original and repackaged US covers is Kiersten Brada, who also portrayed Tessa in the trailer. Jem is portrayed by Yoshua "Yoshi" Sudarso and Will by Skyler Hart in the trailer, which was in turn produced by Dirty Robber and directed by Charles Haine.
- The book is told from several points of views, namely: Tessa, Will, Jem, Charlotte, Henry, Sophie, Cecily, Gabriel, Gideon and briefly in Mr. Sallows and Aloysius's.
- In this book, Will gives Tessa a copy of A Tale of Two Cities with a letter that he signs off with "Will Herondale"; in City of Lost Souls, Jace finds the same book, but the inscription ends with his full name, "William Herondale".