Summary
Highlights
Seth, an animal control worker, develops an obsession with Holly, a girl he encounters on a bus. He attempts to approach her multiple times, at her workplace and a bar, but she consistently rejects his advances. Seth's persistent stalking leads him to find Holly's diary after Eric, Holly's ex-boyfriend, punches Seth for bothering her. Reading the diary, Seth discovers Holly's deepest secrets, some of which disturb him.
Seth constructs a cage in a secret basement at his workplace. One night, he abducts Holly and imprisons her. Initially, Holly is terrified, but Seth believes he is saving her. He reveals that Holly's 'friend' Claire is a hallucination of a person she murdered, exposing Holly as a serial killer. Seth witnessed her committing these murders and intends to prevent her from harming anyone else, which surprisingly moves Holly.
Holly begins to manipulate Seth, first by feigning remorse and then by demanding her release. After nearly harming herself, she feigns a dream about them together, prompting Seth to retrieve snacks. During this time, Seth's colleague, Nate, discovers Holly. Under Holly's instructions, Seth brutally murders Nate and disposes of his body, covering up the crime as Nate's disappearance.
Seth is consumed by guilt, but Holly reassures him, claiming that the first kill is always the hardest. When a detective investigates Nate's disappearance, Seth struggles to maintain his facade. Holly, still manipulative, demands proof of Seth's love by insisting he cut off a finger. Seth complies, only for Holly to use the opportunity to escape the cage. She then slices his throat. Later, it's revealed that Holly is back with Eric and has stopped killing others; instead, she keeps a severely disfigured Seth captive, channeling her murderous urges onto him, stating that he saved her and that's why she loves him.