The previous wave of piranha attacks finally came to an end, when scientists were horrified to find that the upside-down piranha were still in the primary form of cubs, and God knows what would happen when they grew up. The last tragedy left a deep shadow on Shelby (Danielle Panabaker Danielle Panabaker). Shelby felt strongly uneasy when she learned that her uncle was going to build a large luxury water park somewhere. Sure enough, the unreliable uncle directly introduced the nearby lake in order to save money, and a large wave of piranha followed, and for them, a gluttonous meal was about to begin. In the face of people screaming and crying, Shelby's strong sense of justice made it impossible for her to sit idly by. Bravely, she and her surviving companions launched a vigorous rescue campaign.