As Mike Milch and Barry Norris, two unremarkable office workers at Belko Industries in Bogotá, Colombia, step into their workplace, they are greeted by an alarming sight: unfamiliar security guards are turning away the local Colombian staff at the entrance. The atmosphere is thick with tension as they're informed that every employee has a tracking device implanted at the base of their skull—a measure intended to mitigate the risk of kidnapping. Little do they know, this unsettling revelation is just the start of their harrowing ordeal.
Evan Smith, the head security guard, is unaware of any irregularities concerning the new guards, but soon the situation escalates dangerously. A disembodied voice crackles through the intercom, presenting a chilling command: kill two of your colleagues or face dire consequences. Initially dismissing this as a cruel joke, the employees quickly realize the gravity of the threat when, following the refusal to act, four coworkers suddenly suffer gruesome deaths as explosives embedded within their tracking devices detonate, leaving nothing but chaos in their wake.
As panic stirs within the office, Mike attempts to remove his tracker with a box cutter, but he is forced to cease when the voice warns that his own explosive could go off if he continues. A ghastly ultimatum is then delivered: unless thirty people are killed within two hours, sixty lives will be forfeit next.
Amid the growing tension, the employees divide into factions. Mike stands firm with his group against the bloodshed, while Barry, accompanied by executive Wendell, and colleagues Terry, Antonio, and Bradley, plot to gain access to weapons by breaking into the armory. Meanwhile, Mike, alongside his girlfriend Leandra Florez, Evan, and other coworkers Keith, Leota, Peggy, Vince, and Roberto, desperately try to send a cry for help by hanging distress signals from the rooftop. Their frantic attempts are met with gunfire from soldiers positioned outside.
A brutal confrontation occurs when Barry's group ambushes Mike's faction in the stairwell, leading to Evan's tragic death and the theft of his keys to the armory. Armed now with weapons, Barry and Wendell force thirty employees, including Mike and Peggy, to kneel in line. As Barry starts executing them one by one, Dany, who has been hiding in the basement, cleverly restores darkness by shutting off the building's lights, giving Mike and the others a crucial chance to evade more killings.
The office spirals into a state of madness as the violence intensifies. Barry and his followers unleash a hail of bullets, leading to further casualties. In a shocking twist, colleagues Bradley and Antonio become targets themselves, meeting merciless ends at the hands of their coworkers. Dany and Roberto find temporary refuge in the elevator shaft, navigating the horrors unfolding around them. With each passing moment, the atmosphere grows increasingly sinister, revealing Belko Industries as a crucible of human savagery, with the fate of its remaining employees hanging by a thread.
As Barry and Wendell continue their deadly pursuit, the ominous voice informs them of the death toll: 29 lives lost. With only an hour left, they must claim 31 more, which tragically includes Terry, Leota, Peggy, and Keith, leaving a scant 16 survivors. The voice chillingly states that the individual responsible for the most deaths in the next hour will be spared. During the chaos, Barry encounters Dany and Roberto trapped in the elevator shaft, resulting in a grim end for Roberto as the ascending elevator crushes him.
In the meantime, Leandra uncovers Marty and Chet scouring for unexploded trackers to execute their deadly plan. They aim to create a massive explosion to breach the building, but their sinister intentions are thwarted by Wendell's relentless killing spree. In a final confrontation, Leandra manages to take Wendell down, leaving a meager six survivors: Vince, Mike, Barry, Dany, Leandra, and Liezle, whose fate soon follows.
In a fit of rage, Mike strikes Barry down with a tape dispenser as the building’s seal is finally broken. Soldiers escort Mike, the lone survivor, to a nearby hangar, where he comes face to face with the mysterious voice's owner. This enigmatic figure discloses their involvement in an international organization dedicated to studying human behavior, revealing a panel that corresponds to the fallen 80 employees. In a moment of cunning, Mike secretly places the trackers collected by Marty on the soldiers and the voice itself, flipping every switch besides his own. The resulting explosions obliterate the soldiers, severely injuring the voice before Mike retrieves a firearm, systematically eliminating the remaining threats.
Emerging into the open air, Mike realizes he is merely one of many survivors from similar experiments, all under constant surveillance. A new voice echoes: "> End stage one. Commence stage two."
