Emily boards an isolated riverboat with her family for her golden-child brother's birthday, only to be plagued by vivid visions of a prehistoric beast lurking along the waterway. Her self-absorbed stepmother and dismissive relatives brush off her warnings as petty jealousy, steering their tourist vessel straight into a secluded marshland.
When a massive reptilian predator decimates the boat, Emily leads the surviving family members onto a muddy river island, braving toxic fauna and flash floods. As her cowardly relatives repeatedly betray each other to save their own skins, Emily must outwit the ancient creature to guide her father to safety.
