Nancy Adams, portrayed by Blake Lively, is a medical student on a personal retreat to a picturesque beach, a beloved location of her late mother who succumbed to cancer. Transported by a man named Carlos, Nancy initially planned to share this experience with her friend Anna, but unfortunately, Anna falls ill, leaving her to venture alone.
Equipped with her surf gear, Nancy eagerly paddles into the vibrant waves, joining a couple of discerning surfers who recognize her as a newcomer. After enjoying the gentle swells, she connects through video chat with her sister, Chloe, to share her excitement about the paradise-like beach, reminiscent of their mother’s fond memories. Their father, Brett Cullen, expresses his worries for Nancy while acknowledging the heartache she’s endured.
As Nancy ventures further into the ocean depths, a devastating encounter occurs when a great white shark strikes her, causing her to crash into the water and inflicting severe injuries to her leg. Managing to escape to a nearby rock for safety, she quickly improvises a tourniquet with her surfboard's ankle strap to stem the bleeding. Attempting to signal the other surfers for help, she realizes they are oblivious to her plight. In a heartbreaking twist, while calling for assistance, she witnesses the shark gruesomely attack a intoxicated man on the beach who tries to take her belongings.
Facing the lonesome waves as night approaches, Nancy struggles against the cold and pain, even trying to stitch her leg with her jewelry. Morning arrives, and as the two surfers return, she desperately tries to warn them of the lurking danger, only to watch in horror as the shark claims one of them before pulling the other under as well, leaving debris behind.
Calculating the shark's movements, Nancy attempts a daring swim to retrieve a helmet left behind, knowing the risks are great. During this chaotic struggle, she manages to document a message for her family before throwing the helmet toward the beach in search of rescue.
In a moment of cleverness, Nancy fixes the wing of an injured seagull and watches it float away, representing her last tether to hope. Spotting a buoy, she strategizes her escape while evading the shark, which soon turns the buoy into a battleground. After a tense struggle, Nancy cleverly lures the shark into a trap, resulting in the beast getting impaled on a submerged base.
As luck would have it, a young boy discovers her video on the helmet, leading his father, Carlos, to her aid. Though severely weakened and dehydrated, Nancy finds comfort in the sight of a familiar seagull and visions of her mother. She reassures herself with the words, "I'm okay," just before slipping into unconsciousness.
One year later, having healed with a noticeable scar as a reminder of her ordeal, Nancy returns to the beach alongside Chloe and their father, ready to pass on the joy of surfing to her sister, symbolizing her resilience and quest for healing amid the scars of her past.
