A teen finds herself targeted by a creepy substitute teacher who has set his sights on her and will stop at nothing to win her affections.

Ryan Parker becomes obsessed with 16-year-old Carly Bryant when he sees her walking to her high school one morning. He must somehow get to know her. Using teaching credentials, Ryan applies for a substitute teaching position at her school but there are currently no openings. He finds the current substitute teachers list and targets one of Carly’s teachers in hopes he can take her place. After murdering her, he is called in as her temporary replacement.

Immediately, Carly starts to have eerie feelings about Mr. Parker. Her friends, especially best friend Stacey, think Ryan is the hottest teacher to ever walk through the high school’s doors and even joke about what they would do to spend time alone with him. That disgusts Carly but it’s what she expects from her friends.

Her first assignment under Mr. Parker is to do a book report. Being a straight A student, this is a cakewalk for Carly, except she receives an F from her teacher for not doing the assignment the way he wanted it. Ryan gives her a way out - stay after school a few days with him to work on the report and go for a better grade. While Carly has reservations about spending time alone with this man, she sees no other choice.

Ryan learns that Carly has a relationship with a football player, Austin, and grows jealous. He follows Austin home and causes a fatal accident for him. The next thing to interfere in his plans for Carly is the principal telling him that he will be interviewing for a permanent replacement the following week. The principal has a fatal car accident on his way home from a bar, courtesy of Ryan.

Stacey becomes envious of Carly getting to spend time alone with the hot teacher and fails a test on purpose in hopes that she can stay after school with Mr. Parker alone. When Stacey asks her teacher if that would be possible, he tells her it’s not. Stacey grows bold and threatens to go to the new principal about the situation, causing Ryan to back down. He agrees to see her after school starting on Monday, when he actually has different plans for her before then.

Very protective of his plans for Carly, Ryan lures Stacey to a park late at night and kills her, disposing of her body. 

Unable to wait any longer for Carly’s affections, Ryan sends Carly a text, pretending to be Stacey, and having her meet him at the same park. He kidnaps his student and holds her prisoner at his lake house.

The police question Carly’s family and find out from her younger sister Amber that Carly was uneasy with her substitute teacher. With a few people related to the school dying or disappearing since Ryan took the job, the detectives set off on Ryan’s trail and track him to the lake house. Desperate not to lose Carly, Ryan is willing to kill them both, but the detectives arrive just in time to stop him.