A man (Logan Miller) is seen trying to escape a collapsing room by solving a puzzle.
Three days prior, shy physics student Zoey (Taylor Russell) attends a lecture on the Quantum Zeno Effect theory, which states "a system cannot change while you are watching it." Her professor challenges her to take a risk over the Thanksgiving break.
Ben (Logan Miller), seen earlier in the collapsing room, is a stock boy at a grocery store with a smoking habit frustrated at his boss' refusal to promote him to a better role and higher salary.
Jason (Jay Ellis) is a young stockbroker respected among his co-workers for his fast-paced and go-getter lifestyle.
Zoey, Ben, and Jason are all gifted a puzzle box addressed from a trusted acquaintance: Zoey's professor, Ben's boss, and Jason's client. After solving the puzzle, a clue invites them to the Minos Escape Room for a chance at $10,000 should they successfully escape.
War veteran Amanda (Deborah Ann Woll), former miner Mike (Tyler Labine), and escape-room enthusiast Danny (Nik Dodani) arrive and join Zoey, Ben, and Jason in what appears to be a waiting area. When Ben tries leaving the room to smoke, the door handle breaks off, locking the inside and revealing an oven temperature gauge.
After Mike finds a copy of Fahrenheit 451, Zoey sets the temperature to 451°F. Embedded heat panels progressively turn on bringing the room to increasingly hot temperatures, causing panic among all except Danny who refuses to believe the heat is authentic. Zoey notices Amanda's uneasiness and tries to calm her with water from the water cooler. The group receive a phone-call advising them to follow posted rules.
Zoey sees a sign asking for coasters to be used for drinks and the group notice an escape vent to the next room opens when they simultaneously push down on six coasters. Jason escapes first, followed by Mike and Amanda while Zoey realizes filling a glass with water will hold down a coaster long enough for her to escape the room. Ben and Danny rush to cover all coasters with glasses until not enough water remains since Amanda drank a glass earlier. Ben empties his flask into the final glass and the two escape just in time as the room engulfs in flames.
In a mountain cabin, the group, barring Danny, grow concerned at how real the game is becoming. The cameras in each room do nothing when the group needs help. Jason seeks a seven-lettered name connected to "You'll Go Down in History" to unlock the cabin door. Ben has a flashback where he was driving with friends singing "Rudolph the Red Nosed Reindeer" just before a head-on collision. Ben gives RUDOLPH as the code and the group exit and enter frigid temperatures on a frozen stream just as the cabin doors and windows lock shut. Searching their surroundings, Jason locates a door needing a key and the others find a compass, fishing rod, magnet, and ice fishing hole. Jason grows concerned when he recognizes a red parka the group find and take turns wearing to stay warm.
The group fish out a key encased in a cube of ice. Danny attempts to retrieve Ben's lighter to melt the cube but falls into the ice with the lighter and drowns. The group are distraught at the loss of Danny and alarmed at how calculated his death was, noting he fell into the ice when he grabbed the lighter. Fearing hypothermia, Jason convinces the group to huddle and use their collective body heat to melt the ice. Once they retrieve the key Jason manages to turn the lock, but the door does not open. The group escape across the stream into a new door that opens just as all the remaining ice collapses beneath them.
The third room is an inverted bar with pool tables. As the group enter, they feel the entire room elevate to a new altitude. They notice a door without a doorknob; Mike thinks the eight-ball missing from the pool table must be the doorknob hidden somewhere in the bar. A telephone cord drops from the ceiling and the call warns the group to watch their steps. Music begins to play followed by an ear-piercing dial-up sound. Each time the sequence is repeated, a portion of the floor falls away. Amanda climbs up the wall behind the bar and finds a safe with a four-digit code. The group find the numbers they need in a sliding tile puzzle solved by Zoey but cannot open the safe.
Zoey briefly falls unconscious and has a flashback to a plane crash where she was the lone survivor left upside down while everyone was strapped to their seat. All pieces of the floor fall and Mike, Ben, Jason, and Zoey congregate near the exit. Zoey tells Amanda to enter the numbers inverted and in reverse to replicate the room conditions. Amanda successfully unlocks the eight-ball but cannot safely climb across to join the group. Sacrificing herself, Amanda manages to throw the eight-ball to Jason just as she plummets to her death.
The group enter a hospital ward containing beds identical to ones each of the game's players were treated in after being declared as sole survivors: Zoey survived a plane crash, Mike was the only miner pulled alive after a cave-in, all of Ben's friends were killed after he drove drunk, and only Jason was found by the Coast Guard after he and his college roommate's boat overturned in frigid waters. The group learn Danny's entire family was killed by carbon monoxide poisoning and Amanda was the only soldier in her unit to survive an IED blast in Iraq. The remaining survivors realize deliberate planning led to them all arriving at the escape room-to see who would be the luckiest out of the lucky-and aspects of the game have been modeled on their lives.
A TV broadcast states the group has five minutes to live unless they put their heart into it; when time is up, the room will be filled with poison gas. Jason, Ben, and Mike locate an EKG machine to find the optimal heart rate that will lead to the next room. Zoey, wanting to outsmart the game-makers, employs the thinking of the Quantum Zeno Effect and disables all the cameras in the room with the hope of finding a way out. Believing a high heart rate will save the group, Jason inadvertently kills Mike by blasting him several times with a defibrillator. Once poisonous gas begins to leak into the room, Jason hooks himself up to the EKG and lets the poison lower his rate to below 50 BPM. The pathway to the next room opens and Jason and Ben escape, but Zoey refuses to follow along, purportedly collapsing and dying after disabling the final camera.
Jason and Ben enter the fifth room with walls and furniture decorated by optical illusions. Enraged at how Jason callously killed Mike and did not bother helping Zoey, Ben feels Jason was not a sole survivor by choice. Given his behavior in the game, Ben guilts Jason into admitting he deliberately killed his roommate at sea for himself to survive using the red parka. When opening a hatch leading to the next room, Jason and Ben are contaminated by a hallucinogenic substance. Ben finds the antidote injection intended for one recipient and the two fight to the death. Jason breaks Ben's leg but is killed on impact when Ben kicks him into a table corner. Ben escapes into the final room.
The final room returns to the opening sequence of events in the film. Ben manages to contain the flames in the fireplace and use it as a crawlspace to avoid being crushed. He emerges in the final space and is greeted by the Gamemaster, who designs the escape rooms. The Gamemaster explains the purpose of the game, revealing a connecting theme picks the competitors (i.e. college athletes, lone survivors, etc.) followed by individuals betting on winners. Ben hopes he may now leave having won, but the Gamemaster tries to kill Ben to stop the secrets of the game from being revealed.
Zoey manages to have survived by taking an oxygen mask from the hospital bed and connecting its tubing through one of the openings created by the disabled cameras. Feigning death when two cleaners enter Room #4 to remove evidence, Zoey incapacitates them and flees. Zoey manages to save Ben before both kill the Gamemaster and escape.
Ben and Zoey are treated for injuries but all the evidence at the escape room facility is erased by the time Zoey arrives with investigators. Six months later, Zoey convinces Ben to join her on a flight to the Minos Escape Room HQ in New York after she pinpoints their geographic coordinates from their logo. Unbeknownst to them, the game's architect is already one step ahead and planning to trap Zoey and Ben into another game by turning their flight into a simulated escape with a 4% chance at survival.