Shortly after the death of her mother from cancer , medical student Nancy Adams travels to a secluded beach in Mexico , the same one her mother visited while she was pregnant with her. Carlos, a friendly local resident, gives her a ride and drops her off alone at the beach, as her friend who came along with her is staying back at their hotel, recovering from excessive partying. Nancy joins two other locals and the three surf for several hours. Taking a break from surfing, she video-chats with her younger sister Chloe. When she talks to her father in an emotional and strained conversation, it is revealed that Nancy is a senior student but her mother's recent death has caused her to consider dropping out of medical school before graduation. While surfing one last time for the day, Nancy notices the carcass of a young humpback whale nearby. As she rides the last wave back to the beach, a large 23 ft (7.0 m) great white shark knocks her off her surfboard and bites her leg. Nancy climbs onto the whale carcass, but the shark rams it from underneath, forcing her to swim to an isolated rock. She uses her surfboard leash to slow the bleeding from her leg. Later, she uses her jewelry to put rudimentary stitches in place to hold her torn flesh together and the sleeve of her wetsuit as a compression bandage. Nancy is left alone when the unaware locals leave the beach, and she spends the night on the rock with a wounded gull, also injured by the shark, and names him Steven Seagull . The next morning, she gets the attention of a drunk local man on the beach and points to her backpack on the beach. When he finds it, he starts to steal Nancy's belongings then wades out into the water to steal her surfboard and is killed by the shark. Several hours later, the two locals Nancy had surfed with the day before return. They get into the water although she tries to warn them away, and are also killed by the shark. One of the local surfers was wearing a GoPro camera on his helmet. When the shark attacked him, the helmet came off and floated to the surface. Nancy later sees it floating in the water. After some struggle, in which both she and the shark are injured by coral that stings like jellyfish, she is able to retrieve it. While watching footage of the attack, Nancy notices the shark has a large hook stuck in its mouth, possibly from an encounter with fishermen. She uses the GoPro to leave messages for her sister and father as well as information about the shark attack, her injuries, and her location, although she does not know the name of the beach.