Deep in the heart of the Amazon rainforest, a military facility is concocting secret experiments to turn the infamous Candiru fish into a superweapon. However, a disgruntled scientist winds up releasing the mutated beasts into the wild and putting everyone at risk. Soon, a group of Peace Corps. volunteers wind up as prey for the mutant ass-munching monsters, leading to a bloody showdown when the military comes to retrieve their project no matter the cost.