Fifty strangers wake up trapped in a mysterious, dimly lit circular chamber with no memory of how they got there, quickly discovering they're arranged in a ring, unable to move, and that every two minutes an unseen mechanism will execute one of them at random, forcing the group into increasingly desperate and morally compromised alliances to survive. Shot on a minuscule budget almost entirely within a single circular set, the low-budget indie thriller functions as a brutal social experiment, using its premise to strip its characters down to raw self-preservation instinct, prejudice and tribalism. Critics praised its high-concept ingenuity and unflinching willingness to follow its premise to a genuinely dark conclusion. It became a word-of-mouth favorite among fans of tightly contained, ethically provocative genre filmmaking.