As Tessa Gray is drawn deeper into the Shadow World, and goes on the quest of finding her brother, she falls in love with two Shadowhunters–but when it comes to choosing one, trouble begins to brew and suspense finds its way into her life. She will have to learn to hide her feelings if she hopes to survive. However, as her heart rages for love but her mind is bent on saving her brother, will she hide her vulnerable side? Which of the Shadowhunters will win her heart? The next morning, Tessa encounters Jessamine taking care of Nate and Tessa instantly recognizes the fact that Jessamine wished to run away with Nate as he was a mundane. She is later summoned by Charlotte where she overhears the Shadowhunters discussing her brother's fate and she snaps when she hears Will talking indifferently about Nate. The trilogy features William "Will" Herondale, James "Jem" Carstairs, Theresa "Tessa" Gray, and other Downworlders and Shadowhunters. It also features Magnus Bane, Camille Belcourt, and Woolsey Scott and other characters who appear in The Mortal Instruments series. Some time later, another vampire, Lady Camille Belcourt, calls on the Institute and informs the Shadowhunters and Tessa that de Quincey has been secretly throwing parties where he tortured and killed humans by drinking their blood for entertainment, which was a violation of the Accords. The Shadowhunters plan to expose him, but they instantly realize that they need to catch him in the act of breaking the law before making a move against him since de Quincey has been considered an ally of the Clave for so long. Camille admits that her motives for coming forward were revenge against de Quincey who killed her former lover and also to meet Tessa, who has become a famous personality in the Downworld. She also hints that Tessa's brother might be with de Quincey. Jem Carstairs - Will's parabatai, Jem is a ward of the Institute whose life depends on a drug that also slowly kills him.

Magnus Bane - the lover of Camille, Magnus would be a helper to Tessa and the Shadowhunters of the London Institute, particularly Will Herondale. Later, Jem calls for Tessa in his room, and he explains why he collapsed earlier, despite Will's protests that he not do so. When Jem was younger and living in China, a greater demon named Yanluo broke into their home and tortured Jem in front of his parents as an act of revenge against his mother, who had raided the demon's nest and killed its babies. Yanluo tortured him by constantly feeding him a demonic drug— yin fen—that caused him to hallucinate for days. By the time the Clave could step in and stop this abuse, but his parents had been killed and. His injuries were cured, however there was no remedy to his addiction. Jem admits that his body is now dependent on the drug and he has to take some of it every day, causing his skin, hair, and eyes to pale to a silver color, for without it, his body cannot function. He claims that he did not take any dose when he was out with Tessa, which was why he collapsed.He requested that she should not blame herself for his pain. He also tells Tessa that the drug is killing him, but when Tessa asks him why he does not simply give up his dangerous profession, he declares that "there are more things to life than not dying". One evening, she is asked to turn into Emma Bayliss, a girl whose existence is supposedly threatening the sisters. Tessa relives Emma's last few moments alive. The sisters are satisfied and relieved. They inform Tessa that they have been preparing her for an arranged marriage to a mysterious individual known as "the Magister." They expect the marriage to take place that very same day or perhaps the next one. They then depart and Tessa attempts to flee. She wounds the servant Miranda, discovering, in the process that the maid is not a human. Tessa nearly escapes, when she is caught by the Sisters' coachman. The book is told from different points of view, namely: Tessa, Will, Charlotte, and briefly Magnus and Jem.The Enclave gathers at the library to discuss the plan, while Tessa, Will and Jem spy on them. The three learn about Benedict's desire to control the Institute. Meanwhile, in the meeting, the Shadowhunters reluctantly agree to allow Tessa and Will to infiltrate de Quincey's party, while they will wait outside for a signal—another one of Henry's inventions.

Six weeks later, Tessa is held prisoner by the Dark Sisters, training her to " Change", or shapeshift—an ability which Tessa still cannot explain why she has. The sisters give her personal objects associated with the people they want her to Change into, and eventually, Tessa learns to control her power. The series takes place in London England in 1878, a short time after the peace treaties between Downworlders and Shadowhunters. As Shadowhunters consider themselves superior or purer than Downworlders or demons, they may have no qualms about killing either. Will Herondale - Will is the seemingly carefree ward of the Institute who is intent on pushing others away.

Alexei de Quincey - the powerful leader of the vampire clan in London who has been throwing parties to deliberately and publicly renounce the Nephilim Law and the terms of the Accords. Camille Belcourt - a beautiful old vampire and informant of the London Institute who has a score to settle with an old friend, the leader of her clan. The Infernal Devices has been optioned for film by Constantin Film, the same studio that produced The Mortal Instruments: City of Bones. On April 12, 2013, it was announced that Stephanie Sanditz was hired to pen the script for the film adaptation of the book. [6] An update from Cassandra Clare states that the series might be adapted into a TV series. [7] Trivia [ ]

Kidnapped by the mysterious Dark Sisters, members of a secret organization called the Pandemonium Club, Tessa soon learns that she herself is a Downworlder with a rare ability: the power to transform, at will, into another person. What's more, the Magister, the shadowy figure who runs the Club, will stop at nothing to claim Tessa's power for his own.

The next morning, it is decided that Tessa shall remain in the Institute for some more time. The Shadowhunters then discuss their next course of action. Charlotte and Henry decide to visit Axel Mortmain, Nate's former employer and a possible lead. He is also believed to have had connections with the Downworld and subsequently, the Pandemonium Club. Will and Jem are assigned the task to further inspect the Dark Sisters' house. Disinterested, Jessamine volunteers to take Tessa shopping as an excuse to remain excluded from the investigation process. Magnus Bane is temporarily residing in Camille Belcourt's house. Camille has gone undercover for some time, until Alexei's clan did not stop hunting for her. Archer, Camille's subjugate, tells Magnus that he had a visitor. Magnus enters the parlour, only to be met with a distraught Will Herondale, who begs Magnus for his help, which the latter seemingly obliges to. Cassandra Clare has confirmed that " The Infernal Devices has been optioned as a film project by the same people who optioned The Mortal Instruments along with the Walt Disney Pictures." [5] Since it was the same night when de Quincey is supposed to strike, most of the Shadowhunters leave to kill de Quincey in his hideaway in Chelsea. Mortmain, the mundane who informed the Shadowhunters of de Quincey, visits the Institute to tell Will and Jem about the Dark sister who is trying to help the Magister in resurrecting his army and also told them about her location. They rush off to kill her, leaving Nate, Jessamine, and Tessa alone with Sophie, Agatha, and Thomas in the Institute.