เรื่องย่อ…Forced to pay off his debt to the murderous Caribbean crime lord, Tariq, instead, the American scuba-diver and treasure hunter, Jackson Slate, wakes up from its deep hibernation a massive, T-Rex-like sauroid off the coast of Belize. Now, Slate has to team up with diver, Henry, happy holidaymakers, Rod and Jane, and the marine biologist, Sarah Jones, to retrieve a Mayan treasure from the dangerous waters; however, the scaly beast from the sea is ever-present and famished. But, what good is a chest full of gold when you’re dead? Can Jackson and his team defeat the all-powerful reptile, Poseidon Rex?