It starts out like any normal high school drama movie. The main character starts at a new school, runs into another student, helps them pick up their books, then carries on their day just trying to settle in. As it plays the main character finds a love interest and they slowly but surely fall for each other. Then they finally get together about two thirds or three forths of the way through.
Through the whole thing you never get the tell tail "Oh they are acting fishy/weird, I bet they have something to do with the horror part" you are left clueless through the whole thing, guessing but never sure what's going to happen.
Then after the main pair get together, they go home and go to sleep(separately).
The main character wakes up in the middle of the night and goes to the toilet but notices that their little siblings night light isn't on (they never sleep without it and leave their door open). He goes to check his parents room because their sibling would have went there if their night light isn't working.
They quietly knock and upon no one answering walk in. It's a massacre.
Before they can scream they are knocked unconscious. When they wake up they are tied and gagged in their parents room on a chair. The student they ran into on their first day is there in front of them. They go on a crazy rant about how they were destined to be together because of the way they met being like in all those sappy romance movies but the main character had to go and ruin it but getting together with their love interest instead, so they decided to get rid of them and their family so that they would suffer. They raise a gun and then BANG!
Cuts to the love interest waking up in the morning nice and happy from the previous days event of getting together with the main character. They have breakfast and watch the news only to stop in shock at the new the main character had been killed that night with his family. They cry and try to go to their parents which usually sleep in late on Sunday, to find them also murdered.
The last scene of the movie is the love interest standing in shock and horror at the end of their parents bed and in the door frame behind them is the killer that they are unaware of raising their gun slowly.