WARNING: Spoilers ahead for Happy Death Day 2U.
Happy Death Day 2U's ending not only revealed the reason for the time loops that force Tree Gelbman (Jessica Rothe) to repeat the same day multiple times but it also set up a multiverse and a third film. Written and directed by Christopher Landon, the sequel immediately picks up after the events of the first Happy Death Day where Tree solved her own murder and freed herself from being trapped in a time loop.
While the first Happy Death Day was a straight-up horror-slasher film mixed with Groundhog Day's gimmick of the main character repeating the same day over and over, Happy Death Day 2U is even more genre-bending. The sequel retains its serial killer, the masked Babyface Killer, but backburners its horror elements. Instead, Happy Death Day 2U is more of a Back to the Future Part II-inspired sci-fi comedy involving parallel universes. The switch in genres is by design since producer Jason Blum wants each Happy Death Day movie to be different.
However, Happy Death Day 2U is incredibly ambitious with its complex story. As the trailer indicated, Tree is once again forced into a time loop, but it also deceptively claims the Babyface Killer is now after "all of us" and that isn't the case; the advertising hides the film's real story that Tree is also trapped in a parallel universe. If Happy Death Day 2U left you scratching your head, here's our explanation of the time loops, the multiverse, and everything else in this crazy sequel:
Happy Death Day 2U's Time Loop Explained: Origin And How They Really Work
Happy Death Day 2U reveals the cause of Tree's time loop right away: it was all because of a device called the Sisyphus Quantum Cooling Reactor. While the events of the original movie were occurring, Carter's (Israel Broussard) roommate Ryan (Phi Vu) and his lab partners Samar (Suraj Sharma) and Dre (Sarah Yarkin) were working on their science project at Bayfield University's Science and Engineering building. Their device, which they named "SISSY" for short, was designed to slow down time. But they couldn't get the algorithms right and instead, SISSY created a time loop that somehow trapped Tree (SISSY's malfunctions are also responsible for the rolling blackouts that plagued the campus in the first film).
In Happy Death Day, Tree's time loop forced her to relive her birthday, Monday, September 18th, which always ended with her being murdered. After dying eleven times by her count, Tree saved and freed herself when she figured out that it was her roommate Lori (Ruby Modine) who was behind the plot to kill her; when Tree killed Lori, she closed that time loop and Tree was able to move onto the next day. It looked like Tree killing her own killer broke the time loop, but that's not quite accurate.
Tree surviving the day instead passed the time loop onto Ryan, who began repeating Tuesday the 19th at the start Happy Death Day 2U. Ryan had his own Babyface Killer who murdered him, which reset the day when Ryan died. Luckily, Tree knew exactly what was going on (to her chagrin) so she, Carter, and Ryan set out to find the new Babyface. When Tree saved Ryan, they unmasked Babyface and were shocked to find he was a doppelganger of Ryan. Ryan II thought killing the other Ryan was the only way to stop the time loop, so that's why he was killing "himself". Why Ryan II choose to wear the Babyface Killer mask and behave like a serial killer, who knows?
Ryan II also knew SISSY was unstable but Ryan activated it anyway; the device's faulty algorithm caused an overload that hit everyone in the lab - but it was Tree that was most affected. She was sent back to September 18th and into a new time loop - only this time, Tree also ended up in a parallel dimension. There, the rules for the time loop are the same: Tree has to die to reset the day, but this time, she's not the target of the Babyface Killer so she has to commit suicide to force a reset.
Happy Death Day 2U's Multiverse Explained
It turns out, Happy Death Day exists in a multiverse! Most of Happy Death Day 2U occurs in an alternate dimension where Tree has been sent by SISSY's malfunction, which has a variety of big differences to the world she knows. The biggest is her roommate Lori (who is now dead in the original film's universe) is the victim who gets murdered by the Babyface Killer; part of Tree's ordeal is trying to save Lori and each time she fails, she has to die to reset the day and try again, either by making herself the new Babyface's target or by finding creative means to commit suicide.
The full ramifications of the multiverse and Tree's traveling to a parallel dimension are unclear. Tree replaced the alternate version of herself, telling Carter, Ryan, Samar, and Dre that she was both in a time loop and from a different reality. Otherwise, no one noticed Tree was from another universe, not even her parents.
The biggest unanswered question here is what happened to the "other" Tree. Did that Tree take "prime" Tree's place in the first movie's universe, with both trapped in a simultaneous time loop in two concurrent universes (one that only Tree Prime can break them out of)? Or did Tree II get pushed into a third universe, which created a domino effect across the universe? Given Happy Death Day 2U's ending, this doesn't seem to be something the movie is too concerned with.
How Happy Death Day 2U's Parallel Universe Was Different
Happy Death Day 2U's mirror universe is almost completely identical to Tree's "prime" universe except for three key differences: First, Lori is still alive and she is the Babyface Killer's target rather than the person behind the mask. This is because in this universe, Tree never had an affair with her professor Dr. Gregory Butler (Charles Aitken) at the same time Lori was sleeping with him. Therefore, Tree and Lori are actually close friends. Second, Tree's sorority sister and frenemy Danielle (Rachel Matthews) is Carter's girlfriend. Finally, in the parallel universe, Tree's mother (Missy Yager) is also still alive.
Tree actually prefers living in the parallel universe; even though Carter is dating Danielle, Tree is overjoyed to have her mom back. In Happy Death Day, being forced to relive the same day repeatedly forced Tree to realize that she had grown into a terrible person after her mom died three years prior. However, Tree also gradually came to understand that she doesn't belong in the parallel universe; her mother had three years of memories with the "other" Tree that "prime" Tree doesn't have - and she's living someone else's life. Ultimately, Tree had to let go of her mother all over again and she chose to return to her universe to be with Carter.
- Happy Death Day 2U (2019) release date: Feb 14, 2019