In the late 1990s, Clark is struggling to keep his family-owned furniture warehouse afloat while dealing with severe spatial disorientation and insomnia. During a late-night inventory check in the subterranean stockroom, Clark leans against a back wall and physically slips through an invisible threshold, falling into an endless maze of empty office partitions lined with damp yellow carpet and buzzing lights. Terrified, he manages to climb back out through the breach, but discovers his watch and phone display time completely out of sync with the real world.

Desperate for validation, he brings his therapist Mary to inspect the anomaly. When Mary attempts to document the opening, the wall seal destabilizes behind them, snapping shut and stranding both inside the threshold. As they walk in search of an exit, they discover discarded surveyor gear, makeshift chalk arrows left by prior missing explorers, and signs of an organized entity called Async that once attempted to chart the zone.

The maze shifts around them as they wander; hallways suddenly stretch into impossible vertical shafts, and dead ends appear where doors stood minutes earlier. They soon realize they are not alone when a tall, spindly, distorted silhouette begins mirroring their movements from down long corridors. With their flashlights dying and food supplies gone, Clark and Mary follow faint air currents toward a deep drop shaft, leading them into lower subterranean levels where reality breaks down entirely.

In the climax, Clark and Mary discover an old Async research outpost abandoned in the 1980s, containing a malfunctioning low-frequency magnetic stabilizer. Clark realizes the machine is holding the current zone in a permanent spatial loop. As the entity breaches the security doors, Mary creates a distraction using an emergency flare, allowing Clark to manually trip the circuit breakers to overload the machine.

The resulting EMP collapses the room's geometry, opening multiple unstable rifts back to the physical surface world. Clark is pulled upward through a ceiling tear, washing up alive on the floor of a vacant strip mall miles away from his warehouse. However, Mary remains trapped on the other side of the closing rift. The final shot cuts to a surveillance monitor inside an unmarked research lab, where an audio transmission captures Mary's voice still echoing through the yellow rooms, confirming the dimensional rift is expanding across global infrastructure.