‘Old’ Ending Explained: M. Night Shyamalan’s Thriller Will Make Your Head Spin

The last three years have aged all of us rapidly, which makes M. Night Shyamalan‘s 2021 sci-fi thriller, Old—aka the movie about the beach that makes you old—particularly relatable.

If you didn’t get a chance to catch the movie in theaters last year, the good news is that Old is streaming on HBO Max now, free to anyone with a subscription. And sure, the Twitter memes were very funny, but this twisted sci-fi horror story was a genuinely riveting watch. The concept alone, which is based on the graphic novel Sandcastle by Pierre Oscar Levy and Frederik Peeters, is enough to hook you in. And Shyamalan expertly builds on that concept, finding new and visually stunning ways to disturb his audience while staying true to the story.

It’s compelling, fascinating, and maybe a little bit silly, but, as a bonus, it comes with a satisfying ending that actually makes sense—if you’re paying attention. But if you weren’t, don’t worry, because Decider is here to help. Read on for the Old plot summary and the Old ending explained.

WHAT IS THE M. NIGHT SHYAMALAN MOVIE OLD ABOUT? OLD PLOT SUMMARY:

The premise of Old is simple: A group of families on a resort vacation are escorted to a private beach and find themselves trapped there—and aging rapidly. (AKA, the beach that makes you old.)

The protagonists are Guy and Prisca Cappa (Gael García Bernal and Vicky Krieps), who hope that this family vacation will soften the blow to their two young children, Maddox and Trent, that they are getting a divorce. When they arrive at the hotel, Guy and Prisca are greeted with complimentary drinks, which they gladly take. Maddox and Trent make friends with Idlib, the nephew of the resort manager. Trent and Idlib make up a coded language together, and use it to pass secret messages to each other. (Remember this for later!)

A resort guide convinces the family to come on an excursion to a special private beach. They are joined by three other parties: a surgeon named Charles (Rufus Sewell), his vain wife Chrystal (Abbey Lee), their young daughter Kara, and Charles’ mother Agnes (Kathleen Chalfant); husband and wife Jarin and Patricia Carmichael (Ken Leung and Nikki Amuka-Bird), and a rapper who goes by the name Mid-Sized Sedan (Aaron Pierre). The guests are a little confused about why the guide packs an obscene amount of food for their beach day trip, but let it slide.

After discovering a washed-up dead body, it becomes clear that no one can leave the beach. If they try to go back the way they came, they get a black-out-inducing pressure head and are forced to turn back. Then, suddenly, the children are no longer children, but teenagers. As everyone ages rapidly, it becomes clear that most of the adults have underlying medical issues. Prisca quickly grows a huge stomach tumor, which Charles removes. Charles’s behavior is increasingly erratic and paranoid, and it’s revealed he is schizophrenic. Patricia dies from an epileptic seizure and Chrystal—in a horrifying death scene—dies from her bones rupturing from hypocalcemia.

Eventually, the only people left alive are Maddox and Trent, who are now middle-aged (now played by Embeth Davidtz and Emun Elliot).

WHAT IS THE OLD ENDING EXPLAINED?

Trent realizes he still has a message from Idlib that he never decoded. When he decodes it, it says “My uncle doesn’t like the coral.”

Trent and Maddox swim toward the coral and discover an underwater tunnel, and swim through it. We then cut to the scientist (played by Shyamalan himself) who has been observing the people on the beach this entire time. When Trent and Maddox don’t resurface, the scientist calls his superior to report that they both drowned. He assures them there is no way they made it through the coral, and that “trial 73” is complete.

He packs up his recording equipment and returns to a lab. We see monitors tracking things like heart disease, epilepsy, tuberculosis, and more. Then we see scientists injecting drugs into those cocktail glasses given to Guy and Prisca at the beginning of the movie.

The hotel manager gives a speech to the scientists about how many lives they have saved, being able to test new medicines on patients quickly by sending them to the beach, and reducing the time for human trials from decades to a mere couple of days. This trial was a success, because Patricia’s medicine prevented her from having a seizure for 8 hours, aka 16 years in beach time. It is revealed that the scientists don’t know why this beach exists, just that this pharmaceutical company happened upon it, and have been luring people with chronic conditions there for unethical medical trials ever since.

Back the hotel, a sopping wet Trent Cappa approaches a man who he met as a little kid, who he remembers is a police officer. He hands him evidence from the beach—a notebook he found from a previous subject, who described everything that had happened, and the people he was with. The cop calls his station and reads him names from the notebook, who were all reported missing.

Trent and Maddox Cappa loudly announce what happened to them in the hotel lobby. We then flashback to the moment when Trent and Maddox were caught in the underwater tunnel, and see they were able to briefly resurface for air, and then swim the rest of the way out, after the scientist had left his observation post. Trent and Maddox are flown to the airport on a helicopter, where they will meet with their aunt, and live out the rest of their lives having skipped four decades of their life. It’s not exactly a happy ending, but at least now they can prevent anyone else from going to the beach that makes you old.

It’s never explained why the beach makes you old—just that it does. It’s a freak of nature. Just accept it!