Clary Fray just turned 18 and was just hoping to go to a club and hang with her friends. She thought it would be just another day, till everything changed. She then discovers that day that she is a Shadowhunter. A Shadowhunter is a human-angel hybrid who hunts demons. The day that she finds out that she is a Shadowhunter, her mom was kidnapped and had no idea what to do. Jace, a Shadowhunter then takes her back to the institute to learn more about being a Shadowhunter. There, Clary meets Jace's siblings, Isabelle and Alec.
While Clary is with Jace, Alec, and Isabelle, she tries to learn more about her pass. She learns about how her mom has erased her memory anytime she learned that she was a Shadowhunter. Clary then learns about Valentine, an enemy of the Shadowhunters, who wants to raise a demon army by obtaining the mortal cup. The mortal cup controls the demons but no one but Clary's mom knows where its hidden. So Clary then helps the Shadowhunter world to uncover her pass to find the mortal cup.