Seven Tulane University undergraduates – Sara, Nick, Beth, Malik, Maya, Blake and Gordon – drive to Sara's family vacation home on a private lake. There, Sara encounters her old boyfriend, Dennis and his friend, Red. Nick, Blake, Malik and Maya go wake-boarding when a shark attacks Malik. He is able to swim back to shore – missing his right arm. When Nick swims into the lake to retrieve Malik's arm, he is pursued by the shark, barely making it to shore. Being a pre-med student, he stabilizes Malik, and they all take him to the hospital. Blood from Malik's wound attracts a shark that attacks the boat. Maya (Malik's girlfriend who he was about to propose to) is knocked into the water and eaten. The shark damages the steering column of the boat, causing it to crash in front of the boathouse. Sara, Nick and Malik make it to shore. Dennis and Red arrive and agree to take Beth and Gordon to the mainland. During the boat trip, Dennis reveals that he and Red put the sharks in the lake and feed college students to them. Dennis forces Gordon into the water by shooting him; he swims to a mangrove tree but is devoured by a bull shark. Red and Dennis force Beth to strip down and feed her to cookiecutter sharks. Malik arms himself with a harpoon and ventures into the water to kill the shark that killed Maya. His wound attracts a hammerhead shark; he kills it but is further wounded. Nick and Blake pull the shark to shore, and Nick finds a camera attached to its belly. Blake decides to take Malik to the mainland on a jet ski. When they are pursued by sharks, Malik sacrifices himself and later Blake is killed by a Great white shark. Sheriff Sabin visits Sara and Nick and gives them soup, which makes Nick and Sara's dog, who has also eaten the soup, pass out. Sara hears Dennis and Red speaking from Sabin's radio, describing Beth's death. Dennis and Red then appear and take Sara to their boat, while Sabin prepares to dunk Nick into the lake, where sand tiger sharks wait. Sabin reveals that he, Dennis and Red have been inspired by the Discovery Channel's Shark Week and Faces of Death videos to film people being eaten by sharks. Nick is able to break free and ignite a can of gas. Badly burned, Sabin plunges into the lake and is eaten by the tiger sharks. Dennis reveals he is bitter at Sara for running him over with a jet ski, damaging half his face a while back. Red throws her dog into the water and soon after Dennis calls up Carl, the guy from the bait shop, telling him to release another great white shark, Dennis and Red lower her into the lake in a shark cage. As Dennis is about to release her, Nick arrives and takes Red hostage. After a scuffle during which Dennis kills Red in order to catch Nick offguard, Nick shoves Dennis into the water and tries to set Sara free but Dennis appears and tries strangling him. Nick escapes as a great white shark devours Dennis. Nick kills the shark and frees Sara. Nick, Sara, and Sara's dog swim to the boat, having survived. A distance away, a great white shark breaches, signifying that sharks remain in the lake

Twelve-year-old Ann Uekusa and her mother move to the small town of Shimane, where Ann's grandparents live and everyone seems to be familiar with everyone else. Ann soon becomes friends with Daigo, a young boy who lives in Shimane, as well as Fuji and Shika, Fuji's younger sister and her best friend in Shimane. When Ann's mother, Miwako, commits suicide, Daigo helps Ann cope with the sudden change in her life. They fall in love, but Ann's life can only become more complicated when her estranged father suddenly arrives from Tokyo. After greatly contemplating going to Tokyo to live with her father after he asks her, she decides to stay. Ann tells Daigo about her decision but makes her go anyway. Ann and Fuji both live in Tokyo but hardly ever talk because Fuji goes to an elite high school, K High. Ann met back up with her friends she had before moving to Shimane and they continue their friendships. In Tokyo, she ends up becoming closer to Fuji, which causes conflict between her and Daigo.In Shimane, Shika learns the truth about her parentage and in her confusion, she begins to fall in love with Daigo. When Ann returns to Shimane, Shika upsets Ann's fragile emotional state so that Ann and Daigo will break up. In the end, Ann breaks up with Daigo for fear that her own sadness will weigh him down. Ann returns to Tokyo and starts a relationship with Fuji; however, because she does not love him, the relationship does not last. Daigo refuses Shika and rumors begin to circulate that he is interested in his middle school classmate Ayumu, who has been helping him studying to get into university and become a teacher.Nearing graduation, Ann learns that her father and his friend Kaede Kuroki have been dating and she is pregnant with Ann's half-sister. Ann's father and Kaede marry after being encouraged by Ann and Ann's grandmother. Fuji, now aware that Shika was the child of his mother's affair rather than himself, supports her decision to studying abroad in Vancouver so that she can learn not to rely on others. Daigo and Ann make it to the post-secondary institutions of their choice while Fuji must repeat his senior year after running away from home.After attending her middle school reunion, Ann spends some time with Daigo, where he tells her to find her own happiness. Six years later, Ann meets a young businessman named Keiichiro Sakura and they become engaged shortly after. After Ann learns that he only uses people for his own gain, she confronts him about his insensitivity, but he is disappointed in her and breaks off the engagement. Almost a week afterward, she takes a train to Okayama, where Daigo teaches elementary school. Ann's grandmother, meanwhile, believes Ann will suffer the same fate as her mother. After a failed suicide attempt on the beach, Ann is taken to the hospital and later meets Daigo, who asks her to marry him. She says yes and at the very end the two are shown to be happily married with an infant son named Ryo. Meanwhile, Fuji decides to marry his cousin Mariko (against his family's wishes) and Shiika decides to work for her uncle in America.