Characters from different backgrounds are thrown together when a bird strike causes their plane to crash into the Pacific Ocean. Both pilots, along with several other passengers, die in the crash. The remaining survivors, Ava (the daughter of a prominent politician) and her boyfriend Jed, Jed’s friend Kyle, a young girl named Rosa traveling with her grandparents (her grandmother survived), Ava’s personal bodyguard Brandon and flight attendant Danilo, find themselves trapped inside an air pocket at the rear of the fuselage as it sinks to a rock base underwater.
At first, Brandon takes charge, telling the survivors they must stay put and await rescue. On his way to retrieve an oxygen tank from the front of the submerged plane, a large shark attacks Brandon through an opening in the side of the fuselage. He manages to escape back to where the survivors are waiting, but is soon dragged back underwater by the shark.
Kyle’s arm is severely injured in the crash and the girl’s grandmother Mardy ‘Nana’, a former army nurse, treats it in the aft galley with a makeshift splint. Meanwhile, a rescue crew arrives by helicopter to search for the missing plane. The remaining survivors argue over what their next course of action should be, figuring they should do what Brandon would have done. Ava reasons they have 3 or 4 hours of air left before they run out. Jed explains that eventually the structural integrity of the fuselage will not hold and crush them inside. At that moment, the wreckage slides down the rock face, dragging them deeper into the ocean before coming to rest on the edge of a cliff leading into a dark abyss.
The survivors decide to leave the aircraft and swim to the surface. Rosa explains that sharks are afraid of air bubbles and they reason they can scare the sharks away with bubbles from their inflatable life vests. They go in search of diving gear throughout the plane. Meanwhile, the rescue helicopter spots debris from the plane on the surface of the water. Two rescue divers are sent down to investigate the wreckage. They encounter the wrecked plane with the survivors but are attacked by the shark from behind as the survivors try to warn them about the shark’s presence. One diver is dragged off by the shark while the second goes missing.
The survivors search for the second diver and are attacked by the shark which bites off the foot of Jed, who soon goes into shock and dies. Ava retrieves a bag of scuba gear from the baggage area underneath the plane and the survivors prepare to swim to the surface. Kyle explains he’s too afraid to swim to the surface, recounting a moment in his childhood where he dove to the deep end of a pool and was too scared to resurface. Eventually they convince him to leave the plane with them.
The damaged cockpit breaks off and falls into the dark abyss below the cliff. Nana tells Ava to look after Rosa, explaining that she won’t be leaving the plane as she will only be slowing the group down. As the remaining survivors swim through the submerged fuselage to the exit hole, they encounter the shark swimming toward them. Ava uses the bubbles from her life vest to deter the shark from advancing closer and the shark disappears. Kyle takes one last breath of air right before being violently attacked by the shark, allowing the rest of the survivors to exit the plane. They find the missing diver on their way out, apparently having been killed by the shark, and use his oxygen tank for air.
Ava gives the only 2 air tanks to Danilo and Rosa. As they exit the plane, she inflates their life vests and they quickly float to the surface. Ava is about to exit the plane when she spots the shark heading directly towards her. Without oxygen, she manages to exit through the hole, just as the wreckage slides off the cliff and into the dark abyss below, presumably with the shark inside. As she attempts to reach the surface, she runs out of oxygen, but her life vest carries her up anyway, and she miraculously awakens on the surface, surrounded by nothing but the vast expanse of ocean.
She finds Rosa’s stuffed animal floating on the water, but the other survivors are nowhere to be seen. Eventually the rescue helicopter arrives and picks her up, while still carrying the stuffed animal. On board, she finds Danilo and Rosa. The pilot asks if there’s anyone else. Ava shakes her head “no”. Rosa inquires about Nana, but Ava just embraces her and they cry together. Rosa tosses her stuffed animal back into the ocean as the helicopter flies off to safety.