They're back! Every year the population of sleepy Lake Havasu explodes from 5,000 to 50,000 for a single, wild weekend - the 4th of July, a riot of sun, drunken fun and sex-crazed mayhem. But this year, there's something more to worry about than hangovers and complaints from local old timers. Havasu sits in the crater formed by a prehistoric volcanic eruption, and when earth tremors tear open a crack in the lake floor, all hell breaks through. Piranhas - a million ravenous, razor-toothed monsters, unchanged since the dawn of time. Unstoppable killing machines acting blindly under one primeval impulse: to hunt down anything that moves and strip it to the raw, bleeding bone.