Sam wakes up at 6:50 to a text from her boyfriend saying "Happy Cupid's Day". She finds a paper bird by her bed when her little sister comes barging in, asking if she likes the bird she's made for her. Sam mostly ignores her; she takes a shower and gets dressed. She barely acknowledges her parents in the kitchen before she heads out to meet her best friend. Her little sister runs up to her, handing her her gloves, saying she's forgotten them. Sam yells at her saying not to touch her things and takes off in her friend's car. They pick up their two other friends, one of whom hands Sam a condom for her "big night". They giggle and head off to school.
In English class, the Cupid's Day roses are delivered. Sam gets one from her boyfriend with a forced I love you on it, and one special rose (not red like the others but white with crimson edges on the petals) who she guesses to be from her childhood friend. A gay girl declares herself to be in "heteronormative hell", and some of them make fun of a girl with bushy blond hair for not getting any roses (although it is revealed later that she has). At lunch, they see the bushy haired girl and yell insults at her.
They talk about how she peed in her sleeping bag back in fifth grade, and keep making fun of her laughing about how they sent her a Cupid's Day rose with a mean message. The childhood friend catches Sam in the hallway and invites her to the house party he's having that night. Sam rudely declines his invitation and walks away, but it later turns out everybody else is going, so she decides to go as well. Her three friends come over to prepare her for her big night, during which she'll be losing her virginity to her boyfriend, and off they go to the party. When Sam runs into her boyfriend at the party, he is very drunk. He rudely gropes her and tries to lift her top to supposedly clean the drink he accidentally poured on her by licking it. Sam gets rid of her and finds her friends. As they sit together, the bushy haired girl comes in.
They are all shocked at her guts for showing her face at a party like this. Lindsay goes to her and taunts her. The girl calls her a bitch and taunts her back, bringing up Lindsay's family issues. The other three immediately back Lindsay up and start calling the girl names. The girl finally pushes Lindsay, who launches back at her, but they are pulled apart before it can turn into a catfight. Everyone on the scene gang up on the girl, calling her names and throwing their drinks at her. She turns around and leaves in tears.
Sam's childhood friend is late to the scene, but has an idea what has happened, and he blames Sam. Since they're not in the mood anymore, the girls decide to leave the party immediately. On her way out, Sam sees her boyfriend touching another girl inappropriately. As they get in the car, they all vent and curse at what just happened. Just as Sam looks at her phone and the clock reads 12:39 AM, they hit something which sends them off the road flying. Sam wakes up at 6:50 AM the next day as if from a nightmare. She receives a text from her boyfriend saying "Happy Cupid's Day", and finds a paper bird by her bed. She looks confused when her little sister comes barging in, asking if she likes the bird she's made for her.
The rest of the day turns out to be exactly the same, except this time Sam's too surprised to be rude and dismissive to people, and she's not on the scene when the girl is being taunted at the party that night. When they get in the car to leave, she warns Lindsay to watch the road when the time comes, but they get in the accident anyway. After that, the day repeats itself countless times (shown by Sam waking up from the bed and looking out the bed multiple times in one scene), and Sam deals with it in different ways. She stays in bed, skips school, acts out knowing none of it will last, etc.
She tries to stop the accident from happening by not going to the party or not getting in the car, but whatever she does, she wakes up at 6:50 AM to a text message from her boyfriend the next day. She also tries to spend more time with her family, she tries to make it a beautiful day for everyone, etc. but the result doesn't change. In the meantime, she learns a lot about her friends, their pasts, their issues, feelings, troubles...
She finds out that it's the bushy haired girl that they hit on the road that lead to the accident, and in time, she comes to the realization that the only way for her to die and move on is to save that girl's life. She bids everyone goodbye, fixes all her relationships, loses her virginity to the childhood friend who she falls in love with, and after a few failed attempts, she catches the bushy haired girl in the woods before she throws herself in front of the car Lindsay is driving. No matter what Sam says, however, the girl still launches herself to the road, so Sam follows her suit. She pushes the her out of the car's way and gets run over herself, dying immediately.
As the blond girl turns back in shock, saying "Sam, you saved me!", Sam appears in the woods in a peaceful demeanor. She says "No. You saved *me*," and her spirit moves on..