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SYFY WIRE I Know What You Did Last Summer

Exclusive clip: The killer behind Amazon's 'I Know What You Did Last Summer' reveals how they did it

The character behind all the killing reveals how it all came together. 

By Nivea Serrao
I Know What You Did Last Summer Still

It's a tale as old as 1997 time. Teens get into a fatal car accident on the night of their graduation party. Teens hide the dead body and agree never to tell anyone about what they did. Then teens get slowly attacked and killed off one by one, as a mysterious serial killer comes after them. Amazon's revival of I Know What You Did Last Summer didn't deviate from those particular elements of the teen slasher classic, though showrunner Sarah Goodman (AMC's Preacher) did switch a few things up.

First of all, unlike the Jennifer Love Hewitt and Sarah Michelle Gellar-starring movie, the victim of the hit-and-run was Lenon, the more extroverted, fun-loving (and chaos-causing) identical twin sister of the driver of the car, Allison, both of whom are played by Madison Iseman (Jumanji: Next Level).

However, there's a slight twist, as none of Lennon's childhood friends — who were also in the car when the accident occurred — know that it was her who died, and instead think it was her sister, Allison. This switch-up leads to the original Allison choosing to take on her sister's identity and living as her, with only their father now aware of the truth. 

When Allison (pretending to be Lennon) returns home for the summer after her first year of college, she and the rest of Lennon's friends are targeted by a mysterious killer who seems to be texting them from "Allison's" phone. Only, as they discover when her body eventually washes up to the shore, it's not "Allison" seemingly come back from the dead to haunt them. It's someone else entirely.  

Spoiler Alert: The following details the events of the season finale of I Know What You Did Last Summer

Amazon's 'I Know What You Did Last Summer' Reveals How They Did It

As the events of the season's final episode reveal, the person going after everyone was none other than Lennon's best friend Margot (Brianne Tju, Light as a Feather). Not only had she figured out that Lennon was the twin who died (based on Allison's attempts at keeping up her sister's social media activity), but everything she'd done was an attempt to seek justice for Lennon and get Allison to admit who she really was and that she'd been living a lie all this time. But the more Allison maintained the lie — and the more it seemed like Margot's murderous secret was at risk — the more Margot (and her accomplice bodyguard) went after other people. 

Watch the exclusive clip (above) to see just how she carried off every kill over the show's eight-episode first season, and managed to frame their friend Dylan (Ezekiel Goodman) for the murders. Then stream all eight episodes on Amazon to put the pieces together.