This book begins with the main character Clara and her best friend Simon In line too night club. Before they get In she spots a cute boy with blue hair who tells the bouncer he Is a vampire hunter as he enters the club. When Simon and her get In she sees the boy again only this time stalking a girl with black hair through the club and following her into a storage area. Clara notices that he was being followed too and one of the two guys has a knife in his hand. Scared for the boy she wanders after them to make sure he stays safe.
She sneaks into the area and starts to eavesdrop on he conversation that they are having. They talk about things like demons, the Clave, and someone named Valentine. She also finds out that the two guys who followed the blue haired boy are named Aleck and Ace. They tie up the boy and right before Ace can stab him Clara shouts out for them to stop. While they are pondering on her the boy tryst to get away but Ace grabs him, kills him and he disintegrates. They all start asking her strange questions about night children and debate whether or not to take her to the Institute.
Finally Simon shows up with security guards but they can only e Clara and no one else. We find out after at her house that her father Jonathan died in a car crash before she was born her mother keeps his valuable things in a box with the initials J. C carved into it. Later Clara goes to a coffee and spots Ace leaving so she follows him out into an alley. He informs her that a southerner is a person who kills demons, that a downward is magical folk like warlocks, faeries, zombies, vampires, and werewolves, that a mark is a magical rune on the skin giving special powers, and that Hodge is his mentor.
In that moment her mother calls her ailing her that she needs to stay at Simons tonight and then the phone cracks and shuts off. Clara gets scared and runs home where she gets attacked by a centipede snake Like creature and gets saved by Ace. He puts a mark on her and takes her to the Institute. She gets Introduced to everyone Including Isabella, Aleck, and Hodge. Isabella and Aleck are siblings and the rest of their family Is In Doris. He tells her about the rise and fall of Valentine and the circle and the mortal instruments.
She finds out that her mom was married to Valentine and that she could possibly have some headhunter in her. They also realize that her memory has been lost that has anything to do with their world. They tell Simon about everything that is going on. As more stuff is learned she Is told that only the silent brothers in the city of bones can bring her memory back. Ace and Clara get close and even kiss after a picnic Ace had set up for them. Simon does catch them and then confesses his love to Clara. She gains her memories back and is now even more confused than before.
They find the mortal cup and take It to the institute. Hodge ends up betraying Ace and the others and lets his bird Hugo claw her face as Valentine shows up sets Hodge free and takes the cup and Ace through a portal. She gets away and Is found by her mom’s friend Luke who we find out Is werewolf. She Is told by him that the J. C she always thought was her father was actually a brother she never knew that was killed in a fire and Tanat valentine Is near Tanner. Seen Ana Luke go on a aunt to Tina Ace Ana valentine Ana they do in an abandoned hospital. Clara finds her mother in a coma state on a bed and leaves her with Luke.
Clara finds Ace in a room but by his free will. He tells Clara that she has found out that his father isn’t dead either. His father is Valentine. Clara is shocked to find out that the boy she was falling in love with is her brother who is not lost and was not killed by a fire but Ace. Valentine tries to feed Ace lies about how their mother abandoned him and Clara chimes in to call him a liar. This starts a fight which Luke comes in right on time to only make it a bit worse by making Valentine want to stab him. Ace tries to block every Jab that his father throws at him.
He holds a knife to his father’s throat to tell him he better stop. He finally grabs the cup and heads to a mirrored portal to Doris. He tells Ace to come with him but right here is lace’s home. So Valentine leaves and shatters it so no one can come after him. Ace picks up a shard of glass feeling a tad guilty he didn’t kill him when he had the chance. He tends to look at the piece hoping to get a glimpse of his father. At the very end Ace takes Clara on a vampire motorcycle bike ride above New York and she keeps her eyes open this time so she can see everything.