Charlotte: Twenty-two year-old Charlotte runs the entire Institute with a capable hand. Kind and loving, she does her best to care for the orphaned Shadowhunters who live under her roof while hiding her loneliness from the absent-minded husband she loves. It seems as if there's nothing Charlotte can't manage — until Tessa's search for her missing brother begins to uncover a web of corruption and deceit in London's Downworld that threatens to tear London's Conclave of Shadowhunters apart.

Henry: Absent-minded and brilliant, Henry spends his waking hours in the crypt of the Institute, inventing fabulous machines and weapons out of cogs cams and gears. Unfortunately just as many of Henry's inventions don't work as the ones that do, and Henry is as likely to set himself on fire as he is to invent something new and amazing. When Tessa finds herself followed by a silent band of assasins who turn out to be automata — human beings made from clockwork parts — it is Henry who must decipher how they work in order to find the demonic mechanical genius at the heart of the most evil plan London's supernatural world has ever seen.