This is apparently a young adult novel, but it really didn't feel that way to me. It felt more like an adult novel that happened to have teenagers as the main characters.
As far as Clary knows, she's just a normal teenage girl living in New York. Her father died in a car accident before she was born, her mother is an artist, Luke is a close family friend, and Simon is her best friend. All that changes the night she goes to a club with Simon and sees three teens kill another teen they claim is a demon. When Simon returns with a bouncer it becomes clear that she's the only person who can see any of the teens.
Not long after that Clary's mom abruptly announces they're going away for the summer. Angry, Clary storms out and goes with Simon to listen to his friend's band play. She ignores her mother's repeated calls and when she finally does answer, she realizes something is very wrong. Her mother sounds panicked and all but screams at her not to come home.
Fearing her mother is in danger, she immediately returns home to find her mother missing, their apartment ransacked, and a demon inside. In order to find her mother she has to enter the realm of the shadowhunters.
The shadowhunters are raised to kill demons and downworlders who attack humans. Downworlders are part human and part demon (werewolves, vampires, etc). They use magic by carving runes into their skin with a stele, runes that leave a faint scar.
Gradually Clary learns that almost nothing is what it seems or what she thought it was.
I liked all of the main characters, although Simon occasionally got on my nerves. I normally like the shy, geeky type, but the vast majority of the time he was pretty passive. That's not to say he was entirely useless, he often thought things through in a way no one else did and it certainly saved their lives more than once. But he didn't have a forceful personality at all and the other four characters had strong personalities.
I really liked Alec and I liked that Clare included a gay character. I'm not sure I totally get why it was so looked down upon by other shadowhunters though. They didn't have the mortal cup to make more shadowhunters anyway so breeding shouldn't be an issue.
Isabelle was the requisite mean girl, but it was obvious she cares very much for her brother.
I liked Jace, too, even if his badass/broody male thing became very juvenile at times, especially when he was fighting with Clary. But he also had a few moments of humanity which made him seem like more than just a one dimensional character. He could even be sweet, at times. I really liked his chemistry with Clary.
I like the world Clare's created, and all the intrigue that goes with it. I guessed the big reveal before the end, but only a chapter or so beforehand. I'm really curios to see how it will affect everything in the next book.