In the year 2050, the Kepler 822, a state-of-the-art research and drilling facility run by Tian Industries, is suddenly rocked by what appears to be a violent earthquake. As the facility suffers significant damage, Norah Price (Kristen Stewart), a mechanical engineer, along with her colleagues Rodrigo (Mamoudou Athie) and Paul (T.J. Miller), hastily make their way to the escape pod bay in a desperate bid for survival.
Situated at a staggering depth of 36,000 feet, with a crushing pressure equivalent to 8 tons per square inch, the facility is plagued with ominous reports of strange sightings and unexplained occurrences that the Tian company has conveniently brushed aside. These include mysterious explosions and bizarre figures lurking in the dark depths.
As they reach the escape pod bay, they find that all the pods have already been sent to the surface. The only person remaining is Captain Lucien (Vincent Cassel). Together, they navigate to a control base, where they encounter Emily Haversham (Jessica Henwick) and Liam Smith (John Gallagher Jr.). However, their attempts to establish contact with the surface are futile, as the power core of the Kepler is dangerously overheating and poised for catastrophic failure.
Thinking quickly, Lucien proposes a risky plan: they must don pressurized suits and trek across the ocean floor for a mile to reach Roebuck 641, hoping to find a means of escape. The mission begins with an elevator descent into the abyss, but tragedy soon strikes when Rodrigo's faulty helmet implodes under the immense water pressure, claiming his life.
Amid the chaos, the group spots a distress beacon originating from a trapped escape pod below. When Smith and Paul investigate, they discover a body amidst the wreckage, from which a grotesque creature bursts forth and attacks. Smith valiantly dispatches the beast, which Emily later identifies as a member of an undiscovered species, suggesting their drilling activities may have disturbed a hydrothermal pocket capable of sustaining life in the dark depths.
Continuing their perilous journey along the seabed, Kepler suddenly detonates above them, sending debris crashing down and injuring Smith. Thankfully, Norah and Lucien manage to save him before they can find refuge in an access tunnel, where they can charge their suits. However, they soon realize that Smith's oxygen scrubber is compromised, putting his life in jeopardy amid the toxic fumes.
While traversing the access route, Paul is suddenly attacked by an unknown entity, dragging him underwater before he can be rescued. At the mid-point station, the crew witnesses a formidable drill bit being obliterated—an ominous sign that mankind's ambition to drill deep beneath the ocean was an invitation for disaster.
Just as they prepare to leave, the damage to Smith’s oxygen pod becomes critical. refusing to abandon another team member, Norah, Lucien, and Emily support Smith in his struggle to survive. Tragically, while navigating the ocean floor, a humanoid creature ambushes them and snags Smith into a cavern. Although Lucien rescues him, he is soon overwhelmed. In a heart-wrenching choice, Lucien sacrifices himself to protect Norah from the increasing pressure.
Now alone, Norah arrives at the abandoned Shepard station, where she repairs her damaged diving suit before forging ahead to Roebuck. Along the ocean bed, she reunites with Emily and Smith, helping to support him as they enter Roebuck. It’s there they encounter a menacing nest of the humanoid creatures. Despite their best efforts to sneak by, Haversham's oxygen alarm inadvertently alerts the creatures.
In a frantic bid for life, Norah is partially engulfed by one of the beasts but manages to fight back and escape. At long last, they reach the escape pod bay, where Norah discovers only two pods are operational. Acting quickly, she and Emily manage to get the gravely injured Smith into one pod. Norah implores Emily to take the last escape pod for herself.
Just as they are about to escape, a colossal creature surfaces, attacking Roebuck while its smaller counterparts pursue the escape pods. Understanding that her sacrifice may be necessary, Norah triggers a core overload in Roebuck, resulting in a monumental explosion that destroys the creatures and allows the escape pods to break free.
In the aftermath, news outlets report only two survivors from the harrowing ordeal, implying that the remainder of the crew was lost. Meanwhile, Tian Industries separates itself from the calamity, poised to expand its ambitious drilling endeavors further into the depths of the ocean.
