Two sisters, May Louisa Krause and Drew Sophie Lowe, drive to a breathtaking view of the endless ocean, where their car ride unfolds with awkward small talk. Drew shows a genuine curiosity about her elder sister, while May remains quiet and distant, even when Drew nudges her to sing along to “Only You” by The Platters for a touch of nostalgia. It’s clear that Drew has been staying with their mother, and a rift seems to thread through their family history, leaving May feeling distant and withdrawn.
The pair are introduced as deep-sea divers with plans to explore a remote site known among enthusiasts. They reach a rocky mountainside, examine the terrain, and set up their gear before descending to the diving spot. May carries two backup cylinders and a backpack packed with essentials—car keys, mobile phones, and enough equipment for a careful dive. As May assembles her rig with some of the latest gear, Drew tries to draw her into conversation again, but May’s replies stay short and pointed, hinting at a past neither sister fully reconciles.
Once geared up, they slip into the cold water and begin their descent toward the deep caves they’ve chosen to explore. Drew is excited to reconnect underwater with her sister and looks for every chance to savor the moment. They push from fifty feet deeper, negotiating a narrow tunnel that leads them to a comfortable resting spot around thirty feet in. They decide to ascend to a position twenty feet deeper inside the cave, where the water is shallow enough to breathe without masks for a moment. Drew asks May how she’s feeling about the dive, which probes the quiet surface of May’s emotions, but May avoids confrontation and dives back into the water, leaving Drew to follow anxiously.
A thick silence settles as May and Drew press deeper. A landslide from the mountainside has sent rocks crashing into the ocean, and May becomes trapped beneath the debris. Drew’s torch cuts through the murk, but visibility is near zero as debris and sand cloud the water, making any search perilous. With no communication available through their devices, Drew descends further, anchoring herself to a rock and threading through the tight gaps to locate May, who signals her presence with a beam of light.
May devises a plan to save herself and her sister: Drew must surface to fetch extra oxygen cylinders and a car jack that could help lift the heavy rock. They agree to a twenty-minute window, a race against time and dwindling air. Drew, initially hesitant, understands the urgency and accepts the dangerous mission. When she surfaces, she discovers that the spare cylinders and belongings are trapped beneath the collapsed rocks, inaccessible from the surface.
Undeterred, Drew climbs to the cliff, breaks the car window with a rock, and attempts to access the trunk, only to find it jammed. She slices open the backseat with a knife in a last-ditch effort, but the trunk remains out of reach. She then consults a map and discovers a nearby house that might hold tools or help. She retrieves the spare cylinders from the car, returns to the water, and checks her oxygen level before spotting a boat on the horizon. With the twenty-minute mark looming, she vents a final burst of hope and descends once more, grabbing one cylinder and plunging back into the depths. The cylinder slips away and sinks, forcing her to improvise a new plan to reach May with the air they have left.
Back in the cave, May wrestles with her inner turmoil as nitrogen narcosis clouds her mind. She notices Drew’s oxygen pipe leaking, adding another layer of danger to their already fragile situation. Dragging the fallen cylinder back into use, the sisters swap oxygen supplies, and Drew reveals the broader plan: she will surface again and return with help. May cautions her about decompressing correctly and warns about the leaking pipe, underscoring the gravity of the moment.
Drew makes a bold choice and heads toward a place she thinks might offer help—a church she spotted on land. She breaks in, searching for anything that could assist with a car issue, leaving an SOS mark on a map in hopes of drawing attention. In the church, she finds a hammer but returns to the car with the intent to smash the trunk, only to discover the trunk remains stubborn. A wooden pole becomes her improvised tool as she searches for a way to shift the boulder.
On the surface, Drew attempts to repair the oxygen line with an air-foam spray as a last-resort fix, then heads back to May with the improvised tools. The situation grows tenser as May’s memories surface—traumatic recollections of her father putting her through harsh underwater breathing exercises to push her beyond her limits—unveiling the root of her fear and the pressure she carries underwater.
With air running low and no easy escape, Drew hatches a final, ingenious plan: use her inflatable BCD jacket beneath the rock as a makeshift airlift. A burst of air escapes as the jacket’s safety valve releases, complicating their access to air. Drew returns to the surface briefly to fetch a more effective solution, intending to re-enter with the spray to seal the valve and fill the jacket with foam to create lift.
In the cave, May’s trauma becomes a driving force—her father’s relentless discipline alchemizes into a fierce determination to survive. As Drew exhausts herself by free-diving to retrieve the last usable cylinder, May stays focused on the breathing chamber they initially discovered, a tiny space whose air has become toxic. May locates a filled cylinder and positions it between two rocks, then breaks its valve to fill the chamber with fresh oxygen—enough to revive Drew.
Drew lies unconscious and unbreathing until May’s quick CPR revives her. The sisters, both exhausted, manage to surface together after a harrowing, breathless return. The final image finds them sitting on the diving platform, wrapped in each other’s arms, a hard-won moment of healing and reconciliation after their near-fatal ordeal.
