The Infernal Devices series is a prequel to the Mortal Instruments and deals with characters related to those in the original series.
In 1878, sixteen-year-old Tessa Gray sailed aboard the Main from New York City to London to meet up with her brother Nate after the death of their only remaining relative, Aunt Harriet. Upon her arrival, Tessa is greeted by Mrs. Black and Mrs. Dark who have a letter from her brother stating that the Dark Sisters are his landladies and can be trusted. Tessa soon learns that the two have plans for her and they are not good. Six weeks after intense training with the Sisters, Tessa learns she has the ability to Change. When given an item belonging to someone, Tessa is able to transform herself physically into that person and recall details of their life and especially their deaths. The Dark Sisters praise her for a job well done and declare that she is ready to marry the Magister.
Tessa tries to escape but is soon caught and restrained to her bed. She Changes herself into the last person she atempted and soon makes herself smaller and is able to loosen her bindings. Upon hearing someone coming into her room, Tessa smashes a pottery jug on the arm of a figure who sees her but doesn't move quickly enough. Tessa soon realizes the figure is a young man not much older than herself. Dressed like a workman with a variety of knives and daggers attached, it is his beauty that causes her to stare. Tessa has just met Will Herondale and he has come to her rescue. The Dark Sisters attempt to stop them from leaving and a battle ensues in the basement where Will is joined by two other guys. Tessa begins to realize that Will and the Dark Sisietrs are not what they seem and is knocked out during the battle.
Charlotte invites Tessa to stay at the Institute and promises her that she and her husband Henry will search for her brother. At dinner, Tessa meets the other Shadowhunters at the Institute, Jessamine Lovelace, Henry Branwell and once again Will Herondale. Henry is an inventor who works on new weapons and armor for the Shadowhunters. During the course of dinner, Tessa demonstrates her ability to the astonishment of her companions. After dinner, Will takes her on a tour of the Institute and shows her the library. Tessa is touched that he remembers her love of books. Will gives her a brief history lesson on the origins of Shadowhunters and gives her The Shadowhunters Codex to read. Tessa later wakes from a dream to hear beautiful violin music. She crosses the hallway to meet James Carstairs. Jem as he is called, was too ill to come down for dinner. Jem and Tessa soon realize that they are both orphans.