Christopher "Kit" Rook is a Shadowhunter who was raised as a mundane, previously unaware of his heritage. He was born Christopher Jonathan Herondale and is the son of the man who called himself Johnny Rook. He and Johnny are descendants of the notorious Tobias Herondale and his lost line.
Kit was raised by his father, Johnny Rook. Unbeknownst to Kit, they come from a long line of Shadowhunters, descended from a secret Herondale line.
Like most Nephilim, he was born with the Sight. When he was young and still going to a mundane school, he saw a pack of werewolves fighting and screamed until the police came arrived and saw nothing. From then on, Johnny rarely allowed him out of the house, except to occasionally help out at their booth at the Shadow Market. Johnny explained to Kit that they could see the Shadow World because they had the "Gift"—his term for the Sight. For good measure, he instilled in Kit a fear of Shadowhunters by telling him that they kidnapped any person with the Sight under the age of nineteen due to their shortage of warriors since the Dark War.
Growing up, whenever Johnny had to entertain clients in their home, Kit was forced to hide in the basement.
Kit was at the Shadow Market one day in August 2012, in conversation with his friend Wren, when he first noticed Jem Carstairs and Tessa Gray, posing as casual customers but were in fact looking into the Rooks, though he paid them little notice. Just then, the Shadowhunters Emma Carstairs and Cameron Ashdown arrived to seek information from his father, making several people, including Wren, either become uneasy or flee the Market altogether. Kit curiously eavesdropped on the conversation, and Emma noticed him, to his father's dismay. Kit himself got scared, remembering his father's exaggerated warnings about Shadowhunters recruiting young, Sighted mundanes.
Later, Emma and her parabatai, Julian Blackthorn, came to their house to question Johnny. While Kit hid in the basement as always, Julian's brother, Ty, saw him. Thinking that Emma and Julian were in danger, Ty attacked Kit and held a knife to his throat, demanding answers. Kit was struck by Ty's beauty and Ty soon realized that he was Johnny's son. Julian, Emma, and Johnny came in shortly after, surprised by Ty's presence. Fearing for Kit's safety, Johnny hastily gave Emma more information and established that he would never help them again.
When Emma killed Malcolm, the wards surrounding the Rook house were destroyed. Mantid demons attacked the house and killed Johnny in the process. Terrified, Kit called Emma for help, and she, along with Jem and Tessa—two people personally invested in the Herondales who had been searching for his line for years—soon arrived to rescue him. Kit was then taken to the Los Angeles Institute; on the way, they revealed to him his Shadowhunter lineage. Kit was disbelieving throughout, until he was able to confirm it when he was able to open the doors of the Institute—a feat only possible if Shadowhunter blood ran through the person's veins. In shock about everything that just happened, Kit demanded to be left alone in his room, while Ty sat outside the door of his room, apparently protecting him.
- Information about Kit's mother may be revealed in future installments.
- Behind the scenes, Kit's existence as the other living Herondale aside from Jace and Tessa has long been teased by Cassandra Clare. He is referred to as the Lost Herondale.