The New Killer, the Big Secret, and Every Other Big Twist in Happy Death Day 2U Explained

Warning: MASSIVE spoilers for all of Happy Death Day 2U lay below!

Now that Happy Death Day 2U has finally arrived, we have full license to tell you everything you're dying to know about the movie. And, well, there's a lot to go over! Even after the first film dazzled audiences, it left one big mystery hanging over our heads: why does Tree get stuck living the same day over and over again? Director Chris Landon promised there was a logical answer for all the insanity, which eventually went on to become the premise for the sequel.

Months passed, and then we finally got the trailer for HDD2U, wherein we learned that there isn't just one mystery but many. Tree is stuck in the same cycle again? There's a different killer?! What the hell is going on?

Luckily for you, I've seen the movie and I know at least 10 words and can string together sentences at a fifth-grade level. (I'm kidding . . . I have a college degree in English — you're in good hands.) Allow me to tell you all the ins and outs of the sequel and what it might mean for the potential third movie. Yes, there's a potential third movie! Anyway, this is your last chance to turn back before I spoil everything.

So, Why Is There a Time Loop?

So, first things first: what's the big mystery that gets solved in the first one? Why does Tree get stuck in a murdery version of Groundhog Day (1993)? Remember that guy who's roommates with Carter (Israel Broussard)? His name is Ryan (he's played by Phi Vu), and he's been working on a crazy machine for his physics thesis. It might be quantum physics. You know, something that screams science. Anyway, his machine is supposed to slow down time, but obviously he's still working out the kinks with his lab partners, Samar and Andrea (Suraj Sharma and Sarah Yarkin). On the night of Tree's big cosmic event, the machine experiences a huge surge, and it somehow throws her into that crazy time loop. That's what causes the whole of the first film, Happy Death Day.

Of course, we know she breaks the cycle by figuring out who her killer is (her roommate!) and killing her instead. If you're wondering where the first one winks at this whole affair, it's when Tree is at her sorority and Danielle (Rachel Matthews) is bothering her about going to the party. There's a rolling blackout, part of a pattern of blackouts that have been plaguing the school for weeks (because of the machine). Danielle rolls her eyes and says, "Our university dollars at work." So sneaky!

HAPPY DEATH DAY 2U, (aka HAPPY DEATH DAY TO YOU), from left: Israel Broussard, Jessica Rothe, 2019. ph: Michele K. Short /  Universal /Courtesy Everett Collection
Everett Collection

What's the Big Twist?

Now you're all caught up, and we're at the beginning of HDD2U — Tree has broken her curse, but now there's another killer, and he's coming after Ryan, who now seems to be the one in a time loop. Ryan catches up Tree and Carter on the situation, and they agree to help.

This new killer turns out to be a Ryan from the future (or another dimension). He's presumably traveled to this realm to kill the original Ryan and to stop him from perfecting his crazy time-bending machine. Just as they're trying to send the other Ryan away, the dean of the university comes in, hoping to shut down the whole operation. The machine goes off again, causing another explosion that changes everything.

Now Tree is once again stuck in a time loop, which is what we see in the trailer. That's because she's actually been zapped to an alternate dimension! Things are mostly the same, but a little different. Carter is dating Danielle (wow), and there's a different killer who is not Tree's roommate. Oh, and Tree's mom is alive.

How Do They Fix Everything?

Basically, the whole group has to figure out how to fix the machine and send Tree back to her original dimension. But she's the only one who can keep track of the algorithms they've attempted. Cue the montage of her dying all kinds of ways (including jumping out of a plane in a bikini). Eventually they figure it out, but Tree feels conflicted. She doesn't want to lose Carter, whom she's fallen in love with, but she can't stand to go back to the dimension in which her mother has died.

HAPPY DEATH DAY 2U, (aka HAPPY DEATH DAY TO YOU), from left: Israel Broussard, Phi Vu, Sarah Yarkin, Suraj Sharma, Jessica Rothe (back turned), 2019. ph: Michele K. Short /  Universal /Courtesy Everett Collection
Everett Collection

Who Is the New Killer?

By the way, if you're wondering who the new killer is, it's Gregory Butler, the hunky doctor whom Tree is having an affair with in HDD. Well, sort of. In the alternate universe, Tree's roommate, Lori, is the one who's sleeping with him. She's not plotting to kill Tree anymore, obviously. Instead, Gregory and his wife have both conspired to kill Lori! They use the same gimmick that Lori was going to use: let loose hospitalized criminal John Tombs and blame him for the mess.

How Does Happy Death Day 2U End?

Tree saves the day, obviously. She saves her roommate and foils the plans of the dastardly Gregory and his wife. Ultimately, she decides to go back to her own dimension. Even though it sucks to lose her mom again, she decides to move on and move forward with her man.

That's basically it! There is, of course, a postcredits scene that hints at a potential third film, but truly, they could leave the legacy here and it would still be a great legacy. In the end (and in my opinion), HDD2U did an incredible job of answering all my questions and expanding the universe. The film also loses its own shackles and spreads its wings! It's not a horror film; it's not a film with a Groundhog Day gimmick. It's a hilarious, tense, emotional, campy ride, and a wild one at that. Now, let's get that third one.