M. Night Shyamalan just announced that his new movie is titled Old, revealing the poster to his nearly 200,000 Twitter followers, but the film's plot has remained a mystery -- until now.

Collider can exclusively reveal that Old is inspired by the French graphic novel Sandcastle by Pierre Oscar Levy and artist Frederik Peeters. An insider told Collider that Shyamalan received Sandcastle as a Father's Day gift and loved the premise so much that he purchased the rights to the graphic novel, which served as a launching point for his script.

Sources say the events of Old are set in motion when a group of people find a dead body on a beach and slowly realize there is something unnatural happening on that beach.

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Indeed, Sandcastle follows a group of 13 people who aren't able to leave a mysterious, secluded beach that hides a dark secret involving time, which is referenced on the Old poster. The graphic novel is described as an existential horror story about the inevitability of death that plays like a Kafka-esque episode of The Twilight Zone or Lost. The graphic novel doesn't really explain the metaphorical mystery at its core, but Old isn't a straight adaptation, which is why it's merely inspired by Sandcastle rather than based on the graphic novel outright.

Gael Garcia Bernal leads an ensemble cast that includes Eliza Scanlen, Thomasin McKenzie, Aaron Pierre, Alex Wolff, Vicky Krieps, Abbey Lee, Nikki Amuka-Bird, Ken Leung, Rufus Sewell, Embeth Davidtz and Emun Elliott.

Shyamalan and his Blinding Edge Pictures partner Ashwin Rajan produced Old with Marc Bienstock, while Steven Schneider served as an executive producer. Production is already under way in the Dominican Republic.

There were actually some clues to the nature of this top-secret project, as an anonymous comment on Deadline's scoop about Bernal's casting promised Shyamalan was cooking up "a castaway/desert island supernatural thriller," while Shyamalan himself actually posted a photo of Sandcastle back in June 2017, saying he was reading it for inspiration as he wrote the script for Glass. And just last week, he posted a photo of himself in front of a beach which could serve as a location for the movie.

As for the creators of Sandcastle, Levy is an award-winning documentary filmmaker who lives in France, while Peeters is a Swiss graphic novelist whose autobiographical tale Blue Pills: A Positive Love Story, about his serodiscordant romance with an HIV-positive woman, garnered critical acclaim.

Universal will Old on July 23, 2021. For more, check out the first poster for Old and Shyamalan's official announcement for the movie.