Clary Fray, played by Lily Collins, leads an ordinary life in Brooklyn until she witnesses a murder at a club. The murder bears a strange symbol, and Clary soon discovers that she is a Shadowhunter, a half-angel warrior who has the ability to see supernatural beings. She also learns that her mother, Jocelyn, has been hiding this fact from her for years.
Shortly after her mother's disappearance, Clary meets Jace Wayland, played by Jamie Campbell Bower, a fellow Shadowhunter, who takes her to the Institute, a home for Shadowhunters hidden in plain sight in Brooklyn. There, Clary meets Jace's adoptive siblings, Isabelle and Alec Lightwood, played by Emilia Clarke and Kevin Zegers, respectively.
Clary discovers that her mother had hidden the Mortal Cup, an ancient artifact that can create new Shadowhunters, and that Valentine Morgenstern, a powerful Shadowhunter who went rogue, is also after the Cup. Clary and her new friends set out to find the Cup before Valentine can, and in the process, they encounter werewolves, vampires, and other supernatural creatures.
Throughout their search, Clary discovers that her memories have been tampered with and that she has a strong connection to Valentine, who happens to be her father. Meanwhile, Jace and Clary develop feelings for each other, despite their complicated familial ties.
In the end, Clary and her friends retrieve the Mortal Cup and defeat Valentine, but not before Jocelyn is rescued from his clutches. The movie ends with Clary and Jace holding hands, ready to face the unknown challenges that await them.
