‘I Know What You Did Last Summer’ Ending, Explained – How a Teenager Turned into a Killer?

Teenage is the age where we start to understand things, learn to explore, and want to enjoy ourselves with our friends as much as we can. It is an age full of energy, enthusiasm, doubts and desires. A group of six such teenagers who have been friends from their childhoods is now graduating high school. Most of them are leaving the town to attend a University while some are staying behind. I Know What You Did Last Summer is about a brutal accident that changes the lives of those six friends forever. 


Graduation Party at Wai Huna Town

It’s graduation day for the high school seniors in Wai Huna. The last day they are classmates, the last day they spend with each other till the next summer. Six childhood friends, Alison, Lennon, Johnny, Margot, Riley, and Dylan, have gathered at Margot’s place along with other graduating students for their graduation party. The party is crowded with people dancing, doing booze and drugs, and enjoying themselves, except Alison. Alison is the twin sister to Lennon, and both are the polar opposite of each other. 

Lennon is smart and popular. She is a valedictorian and is going to attend a top university. Alison, on the other hand, is nothing like Lennon. She doesn’t get along with anyone, neither her dad nor friends. On the party night, she fights Lennon over Dylan, the guy she is in love with. This hurts both of them, and then Lennon goes fight with her dad. Everything turns into a mess, and everyone leaves the party.


One of the Twins Dies

After the fight, Lennon leaves the party with her dad. While Alison is leaving, their friends mistake her for Lennon and get into her car. Lennon has left first and argued with dad on their way home. Her dad gets mad and tells her to get off the car and walk back home alone. She also gets off the car in a rage. Alison and their friends are in the car smoking, drinking, screaming, and playing loud music. Alison is driving, and while talking to Dylan, she hits something with the car. Everyone thinks that it’s probably a goat. 

Riley finds out that it’s not a goat but Alison’s sister Lennon. However, they all think that the person driving was Lennon and the one who died is Alison. Alison plays along with their misunderstanding because she knows if they know the truth, no one will help her. Moreover, everyone always told her to live like Lennon. The friends are freaked out. After talking for a while, they come to a solution. They decide to throw dead Lennon into the caves near the seashore and tell everyone that she ran away.


Murder Spree in Summer Vacation

Everyone in the town of Wai Huna believes that Alison ran away. Her friends went off to universities, and everyone moved on with their lives. Alison is living her life as Lennon now. After being away for a year, everyone return to Wai Huna for summer break. This is when the brutal murder spree at Wai Huna begins. On her first day back, Alison finds a goat’s bleeding chopped off head in her closet, along with a message written with blood on her mirror saying I know what you did last summer and a note with I’m back written on it. She starts thinking that Lennon is back from dead.

She informs her friends about this, and they become concerned. Only a few days later, Johnny and his coach boyfriend are murdered in the school. In the next few weeks, many other people in the town die, including Dale, who had seen the friends on accident day, a police officer, chef Harold, Riley, and her mom. Police are suspecting Kelly, the coach’s ex-wife, and Clara, the cult activist. Margot suspects Alison’s dad and Dylan, and Dylan suspects Clara, while Alison had no clear suspect until she finds out that her dad was previously married to Clara.


‘I Know What You Did Last Summer’ Ending Explained 

The mass homicides in Wai Huna disturb the social peace, and police are now under pressure to find out the criminal. Margot, Dylan, Riley, and Lennon are getting messages from the killer under the name of Alison, but they haven’t told anyone. Turns out Alison’s dad knows about her secret and is helping her to hide it, only to protect her. Alison is already disturbed because of her dad and Clara’s relation when she finds out that her mom is alive, whom she believed to be dead all this time.

Clara, Alison’s mom, and dad, all were part of a cult together. Her dad had left the cult. The people of Wai Huna have started believing that these murders are because of the cult. The police invade Clara’s secret cave and find dead Riley covered in Honey. They also find Clara dead there. When things finally seem to cool off, Margot fakes her own accident. Alison reveals her secret to Dylan, and he goes berserk and confesses to the police about everything they did. Police, however, think that he is mentally unstable. 

There are many grotesque scenes in the series, and in the final episode, in Margot’s cleanly plotted scene, she kills Alison’s mom and attempts to kill Alison. She is revealed as the serial killer behind all the murders. She had understood the real identity of Alison and wanted to revenge the death of Lennon, her lover. Dylan dials police, but when the police arrive, Margot frames Dylan as the killer, and Alison supports her. Dylan goes to jail. Right before the show ends, the dead Riley opens her eyes. Will Riley come back to life? Will Dylan be free? Will Margot be caught? Only the next season can answer these questions.


I Know What You Did Last Summer is a 2021 Mystery Thriller series created by Sara Goodman. It is streaming on Amazon Prime Video.

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Neha Bhondve
Neha is an entertainment writer who enjoys exploring people, culture, and places through travel, books, and cinema.

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