In order to commemorate her mother who passed away early, Nancy (Blake Lively) came to the beach that had a special meaning for her mother and prepared to surf here. The quiet environment, clear water, warm sunshine, and active water birds made Nancy feel that this was a blessed place given to her and her mother by God. While surfing, Nancy accidentally discovered the body of a whale that was attacked by a shark and unfortunately died. This ominous scene foreshadowed the terrible experience she was about to face. The smell of the corpse attracted sharks from afar. Nancy was attacked by a shark and her thigh was injured. After struggling, Nancy climbed onto a reef exposed to the sea, waiting for rescue from nowhere. What's worse, this reef will soon be submerged with the arrival of the tide, which means that by then, Nancy will be completely trapped in the shark's bloody mouth and there will be nowhere to escape.