Prologue
Kit Herondale is visiting the Los Angeles Shadow Market, where his father, Johnny Rook owns a stall. Kit thinks about the Sight, and the unnatural things he had to see because of it. His father sends him to bring some change, and he goes to Wren's stall. They talk about the recent murders associated with the mundanes, when they encounter two Shadowhunters in the Market.
Wren leaves immediately and Kit notices the pair of Shadowhunters proceed to Johnny Rook's stall. Emma Carstairs and Cameron Ashdown retrieve a red piece of cloth from Johnny, which apparently belonged to Emma's mother, Cordelia Townsend. Johnny tells her that there is no clue that can tell them about Emma's parents murder. Emma then notices Kit and tries to talk to him, but Johnny hides him and starts talking about weird scrawlings on the bodies of the dead mundanes. Emma seems interested and he tells her about a clue she'll find the next day near Sepulchre Bar. Once the pair leave, Johnny advises Kit to get noticed less, claiming that the latter is his "biggest secret."
Los Angeles, 2012
Emma and her friend, Cristina Rosales are visiting the Sepulchre Bar, to gain more information about the mundane murders. Emma breaks up with Cameron over the phone and Cristina badgers her about not being tactful enough to hold a relationship intact. After a comment saddens Cristina, Emma thinks of how little she knows the former, though Cristina has been staying with them for two months. While patrolling, Emma thinks of her parabatai, Julian Blackthorn and the Blackthorn family, who are visiting their great-aunt Marjorie. She is quite close to them, and since her parents' death had lived with them in the Los Angeles Institute. Cristina, meanwhile is a Shadowhunter visiting Los Angeles for her travel year. Cristina then asks mma if she believes that the markings on the murdered mundanes' bodies are the same as the ones on her parents's when they were murdered. Emma replies in the affirmative.
Each of them is lost in their own thoughts when they see a faerie trying to steal mundane goods. They make him turn out his pockets and Cristina lets slip that Emma is a Carstairs. The faerie is surprised and mentions Mark Blackthorn but before they can inquire further, he bolts away, followed by Emma and Cristina. During their chase, the pair come upon another mundane dead body and Emma's suspicions about the matched markings is confirmed.
The Silent Brothers are called upon, as well as the Institute's head, Diana Wrayburn. Diana assures Emma that she'll do her best to find out about the scrawlings and requests them to leave. Cristina had surreptitiously clicked photographs of the corpses, which she gives to Emma. Once they are back home, they print clear images and Emma shows her "Wall of Crazy" to Cristina—it was the interior of her cupboard where she kept evidences and clues about her parents' murder. Emma tells Cristina of how she suspects that Sebastian Morgenstern is not her parents' murderer. She then shows Cristina, the rooms of the Blackthorn children, and Cristina confesses that the reason she is visiting Los Angeles is partly because of Mark Blackthorn; she wishes to be part of a team that comes up with a better negotiation with the faeries than the Cold Peace.
Emma goes out for a jog, some time later, to get rid of her anxiety. She is lost in thoughts about Julian again, when she notices Johnny Rook emerging from the Institute. Believing that he has betrayed her secret investigations, she intercepts him, but is promptly summoned back by a furious Diana. Diana reprimands her for mingling with a crook like Rook. She proceeds to inform Emma that most of the murders included fey involvement, which is why the Silent Brothers have banned her from investigating it. Diana keeps lecturing her about how she should not waste her potential and also about Julian's efforts to bring back Helen from where she is exiled in Wrangel Island due to her faerie heritage, when Cristina announces the Blackthorns' arrival.
The Blackthorn kids; Julian, Ty, Livvy, Dru and Tavvy arrive earlier than expected due to an accident caused by Malcolm Fade. They are overjoyed to reunite with Emma, however she feels that Julian is behaving reservedly with her. The children go to sleep and Julian goes to inform their uncle, Arthur about their arrival; Emma tells him to meet up with her later that night.
Julian visits Arthur in the attic; which seems to be the latter's workplace. Arthur greets Julian as Andrew. Arthur looks muddled and confused, something that Julian believes is normal. Julian thinks back to how Arthur always remained unaware of his surroundings, and a long time ago, when he had discovered Arthur's madness, he had called Malcolm for help. Julian sets down his food and leaves. Meanwhile, Emma has a horrifying nightmare about her parents yet again and slips to Julian's room.
She is surprised he didn't visit her but shrugs it off as exhaustion. She falls asleep on her side of the bed with Julian; something which was a childhood habit of theirs, to ward off the nightmares. The next morning, she wakes up to find the bed empty, and finds Julian enjoying the summer morning on the beach. They converse about her parents's death and the new lead she has found; the murder near Sepulchre Bar. Emma hastens to tell him that if her investigations jeopardized Helen's return, she will stop. However, Julian tells her to continue the inquiries.
They return to the Institute for breakfast, but not before Julian begins formulating a plan which involves Jace and Clary helping them out. Later, Emma wakes Cristina up; who is having another dream about her first love, Diego Rosales and her best friend, Jaime Rosales, and introduces her to the Blackthorns. Whilst having food, Emma tells them of the recent murders and how the scribbled language is so unique that even the Spiral Labyrinth cannot translate it. They all decide to help her on this mission, and later retire for their training.
Cristina and Emma are training in the weapons' room, and talking about the Dar War. Livvy who was initially helping Ty go through Emma's proof joins them. While Cristina's attention is diverted, Livvy tells Emma that she wants to set Cristina up with Julian. Emma is disturbed by the thought, but rushes out of the room when she hears commotion. The visitor turns out to be High Warlock, Malcolm Fade. He hands over Arthur's medicine to Julian, but Emma inquires about it. Realising that Julian has kept Arthur's madness a secret, Malcolm changes the topic and Emma forgets about it when she shows pictures of the markings on the dead body to him. He tells her about how it seems to be those of a ceremonial circle. Julian walks away, infuriated.
They proceed to Ty's room where he is still assessing the documents. All the Blackthorn kids and Malcolm lounge about until Ty finds them some results. According to mundane reports, the murders have been happening at the rate of one each month for the past year, and nothing before that. There is nothing common among the victims, except the way that they are murdered, and the location where they were dumped; Ley lines. Emma answers the door again to find a pizza-delivery vampire. He is wearing a The Mortal Instruments t-shirt. Her thoughts drift off to the residents of the New York Institute. The group breaks up and decides to have their food and watch a movie. While talking about love, Julian gets carried away and leaves for some time. When he returns, he sends his siblings to bed. When Emma and him go to drop Malcolm, the latter tells him that the markings aren't protective spells, they are summoning spells.
Some time later, Emma is awoken by Church. The cat leads her to the beach where she finds Julian gazing at the stars. She sits with him and asks him what is bothering him. He confesses that Mark's absence bothers him and sometimes he believes that Mark hates them. He also says that he would have made different decisions, including not being parabatai with Emma. She is severely hurt by his comment as he walks back.
Idris, 2007
Julian Blackthorn kills his father with his own hands. Extenuating circumstances including the changing of his father into an Endarkened warrior compel him. However, his uncle tells him that he has been cursed by the gods. Sebastian Morgenstern has ruined their childhood by making them watch bloodshed at such a tender age.
Endarkened warriors infiltrate the Accords Hall and mass murder takes place. Andrew approaches his children and attempts to lure out Ty. Julian, with scarce any other option, murders his father. Even as Ty thrashes in his arms and blames him for their father's death, Julian is grateful that he is safe. He shudders however, when he thinks of how he is ready to murder his father, if he threatens his loved ones' existence.
Present
The children of the Los Angeles Institute, including Cristina are giving their oral examination, when an unprecedented delegate from the Faerie Courts. Julian immediately rushes to Arthur and inquires about it; the latter replies that they had been sending him several messages requesting a meeting. Julian thinks back about how his uncle had been sane once, when he had accepted the running of the Institute. However, the torture he had gone through during his capture in the Faerieland was destroying his mind. Julian insists that Arthur come down to meet the fey, as the Head of the Institute should. He gives a vial of medicine to Arthur, which instantly helps him focus on his surroundings. The two proceed to meet their guests in the Sanctuary.
Emma is already present in the Sanctuary. She is greeted by Iarlath, a faerie of the Unseelie Court. He introduces his companions as Kieran, a prince and member of the Wild Hunt. She then inquires if Iarlath had been the one committing the murder at Sepulchre Bar; as it was him she had seen that night. Being a faerie, he cannot lie and denies her accusation. They are interrupted by Arthur and Julian. The faeries ask the Shadowhunters for a favor, which they initially deny when Kieran mentions Mark.
The faerie delegation proceeds to tell them about how the recent murders have affected them as faeries have been slaughtered too. The fey of the Unseelie Court had translated the first line of the inscription before the Unseelie King banned them from doing so. Iarlath tells them that he will give them the papers and in return they must conduct an investigation on the faeries' behalf, and once they find the murderer, they must turn him/her over to the Unseelie Court for trial.
Arthur and Julian initially resist, but the faeries offer to release Mark as a part of the deal. Mark enters the Institute but is forbidden to speak until the deal is signed. The Shadowhunters have scarce choice, as the faerie offer to leave Mark with them till the investigation is complete. After that, he can choose to live with them or return to the Hunt. Kieran also puts in that Mark is changed now, and is no longer one of the Nephilim. Arthur intervenes stating that they wanted to spy on the Shadowhunters using Mark but the faeries deny it again. They finally agree to the terms and swear an oath each. Arthur leaves immediately after, claiming a headache, while Diana takes his place and escorts the convoy out. Julian attempts to talk to his brother, but Mark doesn't recognize him and calls him father, before he passes out.
They take Mark to his room, and notice that he is injured. Julian pulls out his stele to heal his injury, when Mark wakes up and thrashes around, seemingly terrified of his surroundings. He doesn't recognize any of his siblings, leaving them all bewildered until Cristina orders them all out. Diana instructs Emma and Julian to take the papers they obtained to Malcolm, for him to examine and elaborate. Cristina re-assures them that her job is to study the faeries and the effects of the Cold Peace.
The pair visit Malcolm but before he can tell them much, they are interrupted by Magnus Bane. Magnus is apparently dropping by for a casual chat about rogue necromancers. While Malcolm goes to give a call to Diana, Magnus talks to the pair about the despicability of the Cold Peace and mentions Helen Blackthorn as well. The discussion gets inadvertently diverted to ley lines, but Malcolm interrupts them halfway. Once Magnus has left, Malcolm guesses that there is faerie involvement in the investigations, and promises to keep it a secret. While they are leaving Malcolm tells them not to depend too much on him, orelse he'll let them down like everyone else.
Ty and Livvy visit Mark in his room and Ty lays a blanket on him. Alarmed, Mark attacks him and Cristina tells the twins to leave. She has a fairly normal conversation with Mark, who is comfortable around her seeing as she doesn't expect anything from him. He says he missed his siblings, yet doesn't not remember it. Before they can discuss further, Mark receives an acorn—a faerie message—reminding him of some promise and saying that none of it is real.
Emma and Julian are returning from Malcolm's when Jules confesses that he made Emma his parabatai for the sole purpose of not losing her. He apologizes for his harsh words the previous night. Before either of them can talk beyond this, though, Emma's phone rings and Livvy calls them back, stating that Mark is behaving weirdly. Once they both reach the Institute, Julian notices his siblings, looking distressed and Livvy explains how Mark screams in everyone's presence except Cristina's. Julian decides to visit his brother alone and Emma leads the rest of them to investigate about the ley lines.
Julian visits Mark but realizes that he is too broken and the Hunt had tortured him mentally as well as physically. Julian tells Mark about his last words to Jules on the day he was taken away and Mark finally realizes that it is no illusion; he was with his family once again. Though Julian is elated, he feels slightly burdened yet again. Meanwhile the gang goes to the library. Ty and Livvy begin arguing about becoming parabatai, when Dru finds a map about the ley lines in Los Angeles.
Cristina takes Emma aside and tells her about everything that had happened in the room. Mark and Julian abruptly enter the room where Mark makes casual talk with his siblings. Mark then notices the map and concludes that it has been tampered with. He is also anxious to gain the younger Blackthorns' approval, something which they readily give. However, things turn downhill when he is informed of Helen's exile. He blames Julian for not trying hard enough and leaves, disappointed and feeling unwanted. Emma consoles the children and once Julian has regained his composure, he takes Tavvy to his studio. However, before leaving, Ty states that he doesn't want Mark to leave and thus hands over one more responsibility to his brother.
Emma takes soup to Julian and Tavvy. There Julian is unsettled due to Mark's behavior but keeps up his charade. Emma is infuriated and goes to confront Mark. However, he is not in his room. Dru informs Emma that he is on the roof. She subtly mentions how their Aunt Marjorie had called her a "butterball". Emma is appalled and after comforting the young girl she goes to meet Mark. She talks to him about how the Blackthorn kids had spent years trying to plead his case, bring him back home. In return, he tells her about how the Fair Folk had forced him to return home. He also tells her about the torture that was inflicted on them. When he brings up his father's death, Emma changes the topic, not wishing to reveal that Julian had killed Arthur.
Mark offers to take her to one of the ley line convergence points, and after a little hesitation at not being able to take Jules, she relented and let him lead the way. Once they collect their weapons, Mark reveals his faerie steed. He allows Emma to drive it, and they fly up in the sky. Emma is scared when she looks at the ocean, but focuses her mind on the task. Mark approves of her riding skills and they plunge into the night.
Once they reach the ley lines convergence point, they begin investigating and find several clues; the grass had been recently walked upon, Mark finds a wallet that belonged to the same mundane that Emma had discovered dead in the alley behind Sepulchre Bar. However, a few Mantid demons discover them and a fight breaks out. Both of them fight for a while, Mark getting injured in the process. Julian and Cristina arrive in the nick of time and the demons retreat. They all leave the place before another disaster hits them, the questions are halted for a while, as danger lurks around the corner.
They pull up near a deserted shack and tend to their wounds. Julian is angry with Emma for going without informing him and trying to fend off a dozen demons alone, and Emma voices her concern of not being a Blackthorn, thus having to prove herself at every step. They experience weird feelings and return to Mark and Cristina. The name of the dead mundane is Stanley Wells and they decide to translate the languages once they reach the Institute.
They then discuss the monitoring of the ley lines and convergence and the summoning magic being performed. Julian decides to inform Diana first and wait for her to take action. He tries to use a stele on Mark but the latter gets irritated and bares his back to show them how the Wild Hunt had carved Marks of the Nephilim with a knife. He states that his Protection rune had failed him in that moment. However, Jules assures him that he will always protect him.
The next morning, Diana informs them that the convergence is being monitored. During breakfast, Cameron calls Emma and tells her that he had been to the Shadow Market the previous evening and had heard someone say that if Emma poked her nose into their business, they would hurt her. Before she can tell the others, Mark enters the kitchen, apologizes for his behavior earlier, and proposes to start over; they readily accept him. They fill in Ty and the others about the Mantid demons' attack, and tell Mark to take Tavvy to the library. After that, Diana takes their oral test and everyone moves to the training room for the physical one. Diana turns on a radio to distract them. Everyone performs well, but when its Ty's turn, Arthur appears and tells him to take off his headphones.
Ty is unable to focus without the headphones blocking out the noise, and deliberately breaks the radio. Mark, who had been watching them, goes to the dummy they had been practicing on and rips it. Both Blackthorn brothers injure their hands but are livid at being told to follow a certain way of fighting.
In her office, Diana discusses the incident with Julian and tells him that Ty wanted to go to the Scholomance and become a Centurion. She advises him to tell Ty about how harsh the Scholomance is. When Julian refuses to do so, wanting to protect his brother, she tries to make him understand that he must not keep secrets. In return, Julian snaps at her, stating that she had her own secrets due to which she refused to handle the Institute, and all the burden fell on his shoulder. Diana is defeated but she does tell him that the number of secrets he kept might break apart the family some day.
Everyone is sitting in Ty and Livvy's room again. Mark tears Tavvy's toy by mistake and Cristina gives him a new one. Meanwhile, the twins find Stanley Wells' address and Julian proposes that he and Emma go and investigate, as they'd be much quicker. Mark has a disagreement yet again and disregards Julian's word, stating that he is not going to listen to anyone's order and will accompany the two for the field mission.
Emma and Julian visit Stanley Well's place. They find the dead body of another mundane named Ava Leigh. A cloaked figure attacks them, and though Emma chases and corners him, he manages to escape. Julian is hurt by an arrow, and falls to the ground, choking. At the Institute, Cristina finds Mark on the roof and he imparts his frustration about being treated as a young boy by his own younger brother. Cristina comforts him and later gives him a hair-cut. He describes the Faerie court to her and they share an intimate moment when Livvy interrupts them and informs them that Jules' life is in danger.