Valentine is apparently to be the villain character in the story. He is a very talented Shadowhunter and becomes parabatai with Luke and married to Jocelyn Fairchild. He creates an organization known as the Circle because he wants to take down all downworlders. As time goes on, he is going to far and betrays the Clave. His failure to act the Uprising encourages him to make a reformation for Shadowhunters. He wants to create Shadowhunters from downworlders. In order to achieve that, he steals the Mortal Cup and performs a black magic. He wants to control Shadowhunters and demons at once.

Jocelyn who disagrees with his plan, steals the Mortal Cup and fleets. Valentine makes a rumor of his death to avoid the Clave to capture him. He comes back in action and commands his comrades to get the cup from Jocelyn. He claims that he is the father of Jace Wayland and Clary Fray.