The cave-set survival thriller is co-written by Montero and Javier Gullon, who penned "The King of the Mountain," a Weinstein Co. U.S. pick-up, and Denis Villeneuve's "Enemy," which screens at Toronto.
Pic marks a move from found-footage to more docu-style genre movies -- focusing the depravity of human nature.
Lensed on the Mediterranean island of Formentera, the remake of Montero's Sitges-screened "La cueva" follows five friends - three guys, two girls - trapped deep inside a cave, with a friend shooting everything on video.
"It's far more interesting to confront the fears and limits of human beings as they confront one other then record their confrontation with a supernatural phenomenon," said producer Juan Gordon.
"At one point in our lives, we've all been in a situation where we say: "I've got myself into a mess. How will I get out of this?'"
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