Elementary school. Those were the days when you made dandelion rings for pretend marriage ceremonies, when you smeared cafeteria food all over bullies who made fun of your friends and when you wet your sleeping bag at summer camp but blamed somebody else. Does any of it matter in the end? For Samantha (Sam) Kingston, it does.
Sam is a high school senior. She's clawed her way up from the bottom rung of the social ladder to become one of the most popular girls at Thomas Jefferson High — thanks in large part to Lindsay Edgecombe, the ringleader of her little circle.
Sam's life revolves around her friends and her boyfriend, Rob Cokran. At home, she just wants to be left alone. But at school, she is the life of the party. She cheats in chemistry, flirts with her calculus teacher and makes stabbing motions whenever Juliet Sykes walks by — even though she's not sure why Lindsay hates her so much. She also makes plans to lose her virginity to Rob on the weekend and studiously avoids any semblance of social contact with newspaper geek, Kent McFuller, a boy who was the groom in their pretend wedding in elementary school.
It's the Friday before Valentine's Day, better known as Cupid Day at Jefferson High. Students send roses with notes to each other. The more roses you have, the more popular you are. Kent is also hosting a party. He's bought two kegs of beer, so despite his middling social status, anyone who's anyone is sure to be there. Already tipsy, Sam and Lindsay show up to the party along with two friends, Elody and Ally. Rob arrives at the party. Unexpectedly, so does Juliet Sykes. Juliet proceeds to tell each member of the foursome exactly what she thinks of them. The girls mock Juliet and pour alcohol on her until she runs away.
Sam's plans with Rob go awry when he gets drunk and angry. The girls leave the party after midnight in Lindsay's silver Range Rover. They've all had too much to drink, and even sober, Lindsay is a bad driver. Sam really shouldn't have been surprised when Lindsay suddenly screams and swerves into oncoming traffic and then into the woods, killing Sam instantly. Sam experiences a sensation of falling through darkness, but wakes up the next morning. Only it's not the next morning — it's Cupid Day all over again.
On the second day (the first day that repeats itself), Sam is in shock. She does few things differently besides trying to convince herself she has déjà vu and drinking more vodka to make the feeling of inevitability disappear. She dies again in the same car crash that killed her the first time.
On the third day, Sam decides not to do anything that might put her life in jeopardy. She feigns sickness, and her mom drives her to school late. She begs the girls to stay home from the party. They have a drunken (but safe) sleepover at Ally's house instead. In the middle of the night, Ally's mom wakes them up. Juliet Sykes shot herself tonight, she says. There was no note. The girls are disturbed but relieved. No note means they won't be called out for bullying Juliet since middle school. Sam doesn't die, but still wakes up on Cupid Day the next morning.
By the fourth day, Sam has decided that nothing she does matters. She wears especially provocative clothing and insults her friends so badly that Lindsay kicks her out of her car and makes her walk to school. She seduces a teacher and lies on a desk while he gropes her. Because she has no one to eat lunch with, she smokes pot with a former enemy in the washroom. When the girls arrive at Kent's house, she pulls an already-drunk Rob into a bedroom with the intention of having sex with him. But before their clothes are completely off, Rob falls into a drunken sleep. Sam leaves him, finds an empty room and cries her heart out. Kent finds her, comforts her and puts her to bed in a friendly, gentlemanly way. Sam begins to fall in love with him.
On the fifth day, Sam makes family her top priority. She tells her friends she's sick and convinces her mom to let her stay home by saying that she broke up with Rob. She also convinces her mother to let Izzy, Sam’s little sister, stay home with her. Sam and Izzy spend quality time together, and the whole family goes out for dinner at their favorite restaurant. At the restaurant, Sam spots Marian — Juliet Sykes's younger sister. Sam decides to stop Juliet from committing suicide.
After her family goes to sleep, Sam sneaks out of the house and drives to Juliet's — but she's already left for Kent's party. Desperate to intercept Juliet before she shoots herself, Sam follows her. By the time Sam arrives, Juliet has already insulted Sam's friends and barricaded herself in a bathroom. Terrified that Juliet may have already killed herself, Sam asks Kent to pick the lock, but Juliet escapes through the window. Sam looks for Juliet in the woods surrounding Kent's house. She finally finds her standing beside a highway. Sam tries to convince Juliet that it's not too late, that life is still worth living. But before Sam can stop her, Juliet flings herself in front of an oncoming vehicle — Lindsay's silver Range Rover. She is killed instantly, as is Sam's friend Elody.
Sam realizes that Juliet's suicide caused the crash in the first place. Juliet only shot herself on the one night the girls didn't attend the party. She needed to confront them so she could work up the courage to end everything. When Sam and her friends weren't there, it took Juliet longer to decide, and she shot herself instead of throwing herself in front of Lindsay's car. Kent handles the situation calmly, and once again puts a distressed Sam to bed. He tells her that because she stood up for him in elementary school (smearing hot lunch all over a bully who teased him for crying about his grandfather's death) he vowed to always be her hero. Sam falls head-over-heels in love with him. She also resolves that tomorrow she will save two lives, hers and Juliet's.
On the sixth day, Sam is relieved that the day repeats itself. She resolves to do everything perfectly. She is polite to her parents and sister. She stops Lindsay from stealing a parking space from a girl who will be kicked off the swim team if she's late for school. She removes the mocking note and the rose her friends were going to send to Juliet for Cupid Day and replaces it with two-dozen roses and a note that reads, "From your Secret Admirer." She doesn't cheat on her quiz. She scrubs defamatory graffiti from bathroom doors. She orders the roast beef for lunch instead of the more socially correct turkey. At the party that night, she tells Rob to strip naked and wait for her in a bedroom — but instead of coming herself, she sends in an amorous young couple looking for some private space. He is humiliated and flees in his boxers. Sam also intercepts Juliet before she has the chance to confront Lindsay and company. In the privacy of the bathroom, Sam apologizes to Juliet for years of bullying. She also learns why Lindsay hates Juliet — in fifth grade, Lindsay wet the bed on a group camping trip and blamed her best friend at the time, Juliet. Juliet never told anyone, even though Lindsay and her gang of friends (including Sam) made her life a living hell for the next seven years.
But Sam's apology comes too late, and Juliet slips away. After locking the doors to Lindsay's Range Rover and taking the keys, Sam goes after her. There's no way she can jump in front of their car tonight. She finds Juliet by the road again. But when Juliet tries to jump in front of a truck, a surprised Sam barely holds her back. Why isn't she waiting for Lindsay? Juliet tells her the truth: It's not about revenge, Sam or Lindsay. She isn't waiting for the silver Range Rover. Any vehicle will do. She runs into the road just as two minivans converge from opposite directions. She dies.
After dealing with the situation (again), Kent drives Sam home. He kisses her. And Sam wakes up on Friday morning. It's the seventh time she'll experience Cupid Day.
Sam tells her parents she loves them. She gives Izzy her grandmother's necklace and hugs her tightly. She cherishes every moment of silliness with her friends. She tries to do her best on the chemistry quiz, tells her calculus teacher to stop hitting on high school girls, and gives her pot-smoking ex-enemy an art book. She flirts with Kent and breaks up with Rob. She drives her friends to the party and then drives the Range Rover all the way back to Lindsay's house to make sure none of her friends will drive drunk. Kent drives her back to the party — but not before the two exchange passionate kisses. Sam waits for Juliet at the door, but Juliet runs away. Sam chases after her. Kent and Sam's friends chase after Sam.
Juliet launches herself into the road as the two minivans converge. Sam runs after Juliet and pushes her to safety. Juliet is still alive, but it's too late for Sam. She is dying for the last time. But this time, she realizes that she's flying, not falling. And it isn't dark at all — her eyes had been closed before.