A group of research scientists, working in an abandoned off-shore submarine facility, appear to have discovered a neuro-stimulant, extracted from the brains of sharks, that cures Alzheimer's disease. However, unknown to the rest of the researchers the project leaders Dr. Susan McAlester(Saffron Burrows) and Jim Whitlock(Stellan Skarsg?rd) have illegally used proscribed gene manipulation techniques to enhance the brain size of the sharks to attain their spectacular results. During a severe storm, whilst the researchers are celebrating their success, the newly intelligent sharks attack their captors in a bid to escape. As a result of the storm and the sharks attack strategy, the research facility suffers a catastrophic structural integrity failure and begins to submerge. The situation becomes a deadly race against time as the survivors, led by shark wrangler Carter Blake(Thomas Jane) and Preacher(LL Cool J), try to reach the surface and safety as the deadly intelligent killer-sharks continue to flood the facility and hunt their prey.