A man named Alderson wakes up in a stark, white cubical room, with a hatch door positioned in the center of each wall, including the floor and ceiling—six doors in total. After exploring the space, he discovers that each adjacent room is identical yet varies in color. Upon entering an orange room, he is swiftly met with his demise when a razor-sharp metal grate descends from above, slicing him into pieces.
Meanwhile, in a separate white room, several individuals—including Quentin, Worth, Holloway, Rennes, and Leaven—convene, all equally bewildered about their predicament. With no recollection of how they arrived or what purpose they serve, they unite in an effort to escape. They soon learn from Rennes that some rooms hold deadly traps, and with quick thinking, he employs a boot to test for danger.
As they journey through the Cube, they encounter a series of engraved numbers at the hatchways; this prompts Leaven to theorize that prime numbers signify hazardous rooms. Despite an initial belief that prime numbers hold the key to safety, chaos ensues as Rennes meets his end from an acid spray in one of the rooms. Tension builds among the group as Quentin, a police officer, interprets their circumstances through a lens of purpose—identifying Leaven as a mathematics student, Holloway as a medical professional and conspiracy theorist, and himself as the rational leader, while Worth remains a guarded figure reluctant to divulge his past.
When they find the mentally challenged Kazan, Andrew Miller, Holloway insists on bringing him into their fold. Yet, Quentin disregards their newfound insights as he suffers injuries that contradict Leaven's initial theory on prime numbers. An atmosphere saturated with distrust and frustration transpires, and tensions heighten when Worth reveals his role in designing the Cube, shedding light on its structure but offering little comfort about their situation.
As they progress towards the edge of the Cube, they are thwarted by traps overhead, and must double back to devise a safer strategy. Their navigation reveals a blue room, where a sound activates the motion detector. However, a mishap occurs as Kazan unintentionally triggers a perilous trap. They soon face tragedy when Holloway attempts to explore a gap only to find herself falling to her death, leading Quentin to manipulate the group dynamics by attempting to sway Leaven towards his agenda.
Time passes as they uncover a staggering truth: the rooms are shifting, nonsensical patterns turning their navigation into a perilous game of survival. Leaven deduces that traps are actually tied to powers of prime numbers, while Kazan's unique ability as an autist savant becomes their unexpected tool for salvation. As the group realizes they are circling back to the same location, their desperate situation escalates, culminating in a confrontation where Quentin's sanity disintegrates into violent chaos.
Ultimately, with Quentin incapacitated and their plans thwarted, Worth embarks on a selfless act, sacrificing himself to protect Kazan. A final peril unfolds as Worth drags Quentin to an end amid the shifting rooms, leaving Kazan as the last standing survivor. As he steps into the blinding light emerging beyond the Cube, the weight of their harrowing journey lingers in the air, showcasing a profound testament to survival against overwhelming odds.
