As Clary Fray, a teenager from New York, starts to experience a series of bizarre events—such as peculiar symbols cropping up in her drawings and her mother's increasing anxiety—she unknowingly uncovers a sinister underworld. During a night out at a bustling nightclub with her friend Simon Lewis, Clary witnesses a shocking murder committed by Jace Wayland and his mysterious companions. The following day, two strange figures, Emil Pangborn and Samuel Blackwell, intrude upon the Fray household, searching for a powerful artifact. In a frantic attempt to protect her, Clary’s mother, Jocelyn, becomes comatose after warning her daughter of Valentine's devious intentions.
Upon returning home, Clary finds her mother missing and is soon attacked by a demonic creature, only to be saved by Jace, a trained "Shadowhunter," who eliminates the beast. As she gathers herself, she learns from Madame Dorothea, the insightful witch next door, about the dangerous motives behind Pangborn and Blackwell's quest for the Mortal Cup. Clary begins to piece together the dark secrets of her lineage, and with Simon in tow, they seek sanctuary at Luke's antique shop, where they discover Luke under siege by the invading duo. Desperate to escape, the group runs to the Shadowhunter Institute, a concealed refuge within the labyrinthine corridors of an ancient cathedral. Inside, Jace tends to Clary’s injuries and introduces her to fellow Shadowhunters, Alec and Isabelle Lightwood, along with their enigmatic mentor, Hodge.
As Clary learns more about the Shadowhunter legacy—individuals who are part human and part angel, tasked with slaying demons—she realizes she has inherited her mother’s abilities, which include the power to inscribe magical runes on her skin temporarily. Valentine Morgenstern, a former Shadowhunter turned rogue, has sinister plans for the Mortal Cup, aiming to rule over both his own kind and the demons they battle. Clary is thrust into the mysteries surrounding the Shadowhunter world, leading her to the City of Bones, where Jace strives to unlock the secrets of Clary's suppressed memories. Through a visit to the elusive Magnus Bane, the High Warlock of Brooklyn, Clary discovers that her mother erased crucial knowledge from her mind, leaving her confused and searching for clarity.
When Simon is captured by vampires, Clary steps up for a harrowing mission to save her friend, joined by Jace, Alec, Isabelle, and a ragtag group of companions. As they delve deep into the vampire and werewolf underworld, Clary finds her personal journey intertwined with ancient artifacts and magical forces that govern the Shadowhunter realm. Meanwhile, as Simon begins to recover at the institute, he undergoes a subtle transformation; he emerges with two puncture marks on his shoulder, indicating profound changes within him, including a newfound ability to see without his glasses.
The complex emotional currents come to a head as Clary and Jace share a kiss, igniting feelings of betrayal in Simon, who professes his love to Clary, only to have his emotions brushed aside. Amidst rising tensions, Clary uncovers the hidden Cup within one of Madame Dorothea's tarot cards—created by her mother—and they soon find themselves facing a demon disguised as the fortune teller. Simon and Jace join forces to defeat the evil imposter, but their victory is bittersweet when Alec suffers a grievous injury.
Clary retrieves the Cup card and the team retreats to the institute, seeking Magnus Bane’s assistance in mending Alec's wounds. However, after a series of betrayals, Clary learns that the malevolent Valentine is, in fact, her father. This revelation shocks her to the core, especially after Luke divulges the truth about her older brother's tragic fate. With the stakes higher than ever, Clary deductively crafts a ruse to outsmart Valentine, sending him spiraling into a portal while successfully maintaining her newfound powers.
In the aftermath, with Jocelyn still unconscious at the hospital, and tensions simmering down, Clary and Jace confront their feelings and the mystery of their relationship. Clary embarks on a new chapter in her life, ready to embrace her role in the Shadowhunter world alongside Jace, as they prepare to tackle the impending challenges ahead.
