Newly arrived at her family's lake-island cabin, college student Sara (Sara Paxton) and her friends prepare for a weekend of fun in the sun. But soon after they dive into the lake, football player Malik (Sinqua Walls) stumbles out of the water with a grievous wound. Thinking Malik is the victim of a freak accident, the friends pile into a tiny speedboat and head for the hospital. To their horror, they discover that they are surrounded by hundreds of massive, hungry sharks.