Clockwork Princess (2013)

Clockwork Princess is a 2013 fantasy novel written by young adult author Cassandra Clare. It is the third and final installment of The Infernal Devices trilogy, following the first book, Clockwork Angel, and the second book, Clockwork Prince. It is written in the third person through the perspective of the main protagonist, Tessa Gray, who resides in the Shadowhunter's London Institute. This final installment follows Tessa and her friends as they face off against the series main antagonist, The Magister (also known as Axel Mortmain), who plans to completely obliterate the Shadowhunter race.

Plot

Two months after the events of the previous book, Tessa Gray is in the midst of preparing for her wedding to Jem Carstairs. Gabriel Lightwood arrives at the Institute and requests help in taking care of his father, Benedict, whose demon pox has turned him into a worm, killing the Lightwood's servants and Rupert Blackthorn, the husband of his daughter, Tatiana. At the end, Gabriel and his brother, Gideon, have no choice but to kill their father, creating a rift between the brothers and Tatiana. Gabriel moves to the London Institute and develops a relationship with Will Herondale's sister, Cecily, who has also taken residence in the institute after failing to convince Will to return home, much to Will's annoyance.

Jem gets sick faster and Will realizes that he has taken an unusually higher dosage of yin fen so he can stay stronger for the wedding. However, Axel Mortmain has bought all of London's stock of yin fen, wanting to blackmail the Institute into handing over Tessa in exchange for the drug. Jem refuses to even consider the offer and convinces Tessa to do the same, so they decide to move the date of their wedding earlier. Meanwhile, Consul Josiah Wayland, now increasingly frustrated by Charlotte Branwell's refusal to be his lapdog, attempts to convince Gideon and Gabriel to betray her in exchange for the Lightwood's honor to be restored. Gideon steadfastly refuses, but Gabriel has to go through some time before he finally chooses to side with Charlotte.

After undergoing trials at Silent City, Jessamine Lovelace is sent back to the London Institute. On the day of her arrival, automatons and Mrs. Black attack the Institute and mortally wounds Jessie before taking Tessa away. Before she dies, she leaves clues for Will and Cecily about where Mortmain is taking Tessa to: Cadair Idris. Jem collapses from his illness and learns about Will's unrequited love for Tessa, before urging him to save her in his stead. While Will is on his way, he feels his parabatai bond with Jem severed and realizes that Jem is gone. Back at the institute, Charlotte's attempt to rally the Enclave to support her fails, managing only to gather Sophie, Cecily, Gideon, Gabriel, Magnus Bane, and three Silent Brothers for the mission to stop Mortmain. Henry and Magnus create a device capable of transporting people through great distances, dubbed as the Portal. Meanwhile, Wayland gathers the Clave for an emergency meeting to depose Charlotte, only for the automatons to attack them and kill him and Aloysius Starkweather.

On the way to Wales, Tessa briefly frees herself from Mrs. Black, now a disembodied head attached to an automaton body, and discovers that her clockwork angel pendant holds an essence of the angel Ithuriel. Upon arrival at Cadair Idris, Tessa is forced to shapeshift into John Shade and teach Mortmain how to create automatons capable of powered by demonic spirits and immune to Nephilim weapons. Mortmain reveals that Tessa was born to a Greater Demon father and a Shadowhunter mother, a feat normally impossible since demon-Nephilim children are usually born dead due to the Marks. By switching Elizabeth Gray with Adele Starkweather, Aloysius' granddaughter who died when she was young, "Elizabeth" grew up to be a Shadowhunter who was not Marked. By additionally giving Elizabeth the protection of Ithuriel, Tessa could be delivered alive. Mortmain arranged for Tessa to start a new race of demon-Nephilim hybrids. Will reunites with Tessa and consummates with her—and in the process, Will receives a star-shaped mark on his skin where it touched Tessa's clockwork angel necklace pendant (a mark that is visible in future generations of male Herondales throughout the Shadowhunters Chronicles and also on others who were touched by the angel such as Clary Fray/Fairchild). Will and Tessa meet up with Charlotte and the others and begin battling through Mortmain's automatons, learning to their shock that one of the Silent Brothers, Brother Zachariah, is Jem. Henry is gravely wounded and left paraplegic, even after Magnus successfully saved him. As Tessa is about to be captured by Mortmain, she shapeshifts into Ithuriel himself (the angel in Tessa's clockwork angel pendant) and incinerates Mortmain, before falling unconscious for several days.

Upon her recovery, Jem, now Brother Zachariah, visits Tessa and promises to meet her every year for an hour at Blackfriars Bridge before departing for Silent City. Charlotte is offered the job of Consul and plans to train Will to succeed her as head of the London Institute. Gideon proposes to Sophie and accompanies her as she undergoes Ascension to become a Shadowhunter. At the Christmas celebration of that year, Magnus leaves for the New World and makes Will promise to find his own happiness. After speaking with Jessamine's ghost, Will proposes to Tessa, who accepts. Subsequently, Will and Cecily introduce Tessa and Gabriel, respectively, to their parents.