We Weren't Expecting That! Here's the Killer in 'I Know What You Did Last Summer' (SPOILERS)

Spoiler alert: This article contains spoilers for Season 1 of I Know What You Did Last Summer.

Have you been dying to discover the killer in Season 1 of I Know What You Did Last Summer? The Amazon Prime original series is a reboot of the 1997 film of the same name. Season 1 follows the same premise as the film — teenage friends are stalked by a killer after they accidentally kill someone.

So who was the killer all along? Does he (or she) get away with the murders? We explain.

It was Margot (Brianne Tju) all along! Episode 8, "Your Next Life Could Be So Much Happier," features a few red herrings before Margot reveals herself as the murderer. What was her motivation? Let's backtrack just a bit.

Allison Grant's twin sister Lennon Grant (Madison Iseman) is killed the previous summer. Allison is jealous of Lennon, but when Allison finds out that Lennon has slept with Dylan (Ezekiel Goodman), the tension in their dynamic escalates because Allison has been crushing on Dylan.

After a fight, Allison gets into Lennon's car with some of Lennon's friends. Allison accidentally hits someone with Lennon's car, and discovers to her horror that she's killed her own sister.

Allison pretends to be Lennon from that point, so her friends think that it's Allison who was killed. In Episode 8, Margot reveals to Allison that she knows Allison has been pretending to be Lennon ever since the accident. Margot has been killing people that Allison loved to frame Allison and also to get Allison to come clean about Lennon.

However, Margot ends up genuinely falling for Allison. As a result of her feelings, Margot gives Allison one last stab at confessing to her deception. Allison doesn't confess, so then Margot actually stabs her.

Margot kills a lot of people without a shred of remorse. Sadly, Margot gets away with it, thanks to Allison and poor Dylan being in the wrong place at the wrong time. Dylan arrives at the scene where Margot has stabbed Allison. When police officer Lyla (Fiona Rene) arrives at the scene, Allison finally has a chance to own what she did (and reveal that Margot is a borderline psychopath).

Allison blames Dylan instead. Season 1 ends with Dylan's arrest. Sure, Dylan has some strange interests, but he never actually murdered anyone. So, Allison's secret is safe for now. She and Margot essentially promise to never abandon each other, but will that last if I Know What You Did Last Summer gets a second season?

Stream Season 1 of I Know What You Did Last Summer on Amazon Prime Video.