Tessa has spent the first sixteen years of her life being overprotected by her aunt after the death of her parents in a carriage accident. She lives almost all her life in books, dreaming of having the kind of adventures the heroines she reads about do—until she is forced to travel from New York to London when her brother Nathaniel goes missing and only a pair of mysterious—and sinister—women called the Dark Sisters seem to know where he might have gone. The Shadowhunters of the London Institute may be Tessa's only hope of finding Nate, but their mysterious world of demons and Downworlders holds many dangers for her—especially when she realizes she might be more a part of it than she'd thought.
Driven to Suicide: Subverted. She makes the Magister think she killed herself so that he wouldn't get his hands on her power, but in reality she Changed into a woman who'd died by a gunshot wound seconds before the wound would prove fatal.
Shape Shifter: This starts off the whole story because of her ability to change into anyone, even possessing some of their memories and personality (she just has to touch one of their items to do it the first time).
Wide-Eyed Idealist: Tessa always compares her adventures to what she's read and hopes for the best of all situations.
William "Will" Herondale
Seventeen-year-old Will is the sort of young man nice Victorian girls were warned against. He drinks, gambles, and enjoys the company of ladies of questionable virtue—at least, as much as he enjoys anything. Will hates everyone and everything, with the possible exception of Jem, and even that's in some doubt. Charlotte despairs of keeping him alive past the age of nineteen. When he finds himself oddly drawn to Tessa, his friends begin to hope that the Downworlder girl will prove Will's unlikely salvation—but as Tessa grows closer to the bleak secret that makes his life a prison, danger threatens to destroy them both if she ever finds out the truth.
All Girls Want Bad Boys: Will constantly says he's always out drinking and gambling, and that there are a dozen girls who've claimed that he'd compromised their virtue. Jem, however, thinks he's lying to make himself look bad.
Brought up in the Institute in Shanghai, Jem's parents were killed by a demon who allowed Jem to live—but with a terrible price to be paid. Frail and silver-haired, Jem seems an unlikely demon-killer, but his skills and swift intelligence make him a formidable foe. He finds a kindred spirit in Tessa as both of them feel they are torn between two worlds, neither belonging completely to one or to the other. As Jem's affection for her grows, will Will have to hurt the only person in his life he's ever seemed to care about?
Dark and Troubled Past: A demon who had a grudge against his mother tortured him in front of his parents, injecting him over and over with a drug that made him hallucinate vividly. See Soap Opera Disease.
Deadpan Snarker: His snarkiness comes mostly from saying something, then adding "Not really" with something humorous. He can play the trope completely straight, though.
Sensitive Guy and Manly Man: The Sensitive Guy to Will's Manly Man, Will's tendencies often making him look near-saintlike in comparison.
Soap Opera Disease: It was caused by a demon drug that was used to torture him and his parents when he was younger. There is no known cure for it, and he has to keep taking a specific drug to keep on fighting - as Brother Enoch says, taking the drug means a slow death, but keeping him off the drug would mean a quick one.
In the Blood: It's mentioned in passing that her father was the previous caretaker of the Institute.
Parental Substitute: Raised Will, Jem, and Jessie since they came to the institute. Will says that she would have been called a governess had she not been so intelligent and if she didn't have the ability to chop one into pieces.
Jessamine's parents, like Will's were Shadowhunters who left the Clave. Their deaths in a fire orphaned her, leaving her to be brought up in the Institute by Charlotte and Henry. Jessamine hates everything about being a Shadowhunter, from the training to the danger to the existence of demons, which she sees as "smelly and disgusting." Armed with a razor-edged parasol and an equally sharp tongue, Jessamine can be dangerous if she wants to be—to herself as much as to the supernatural creatures she's sometimes forced to encounter.
Big Brother Instinct: Will says the reason Gabriel hates him so much is because he compromised the latter's sister's virtue. But then again, it's Will, so we don't know if that's true or not. As of the second book, it's apparently because Will rejected his little sister's advances (in his defense, she was a lovesick twelve-year-old) and broke Gabriel's arm in public.
Heel-Face Turn: He stops supporting his father after his father is turned into a demon by the demon pox.
Thicker Than Water: Gabriel puts strong emphasis on staying loyal to family. At the end of Clockwork Prince, Gabriel chooses to stay with his father while his older brother Gideon deserts him for the Institute. In Clockwork Princess, he finally understands that he was wrong to trust his father so much.
Gabriel's older brother, who returns from Spain in the second book.
The Scapegoat: In all honesty, de Quincey is not the poster boy for morality, but he is certainly not the Magister.
Vampires Are Rich: Known to throw absolutely lavish parties where they abuse mundanes.
Bi the Way: Although most initially know this from the Mortal Instruments series, this series shows it at first with certain comments he makes about Will upon first meeting him and Tessa, and later makes it obvious when he is shown to have started a physical relationship with Woolsey Scott. He's certainly still quite campy even in this series.
Call Forward: Magnus tells Tessa he has a thing for people with blue eyes and black hair. Who has blue eyes and black hair? Alec from Mortal Instruments!
Another one in Clockwork Princess. When talking to a group that includes both Gabriel and Gideon Lightwood and keeps referring to one as the other, he tosses off, "All Lightwoods look alike to me." Just wait a century or so...
Scars Are Forever: She has a huge one running down the left side of her face that distorts her beauty. She seems to be more or less okay with it, though, saying that whoever would love her now wouldn't love her just for her looks.
Legacy of Service: He comes from a long line of people who've had a touch of the Sight, which is required for servants of the Nephilim. Needless to say, his family's been serving the Institute for a while.