Scotty and Dong, a pair of burnout losers who work at a small-town pizza joint, serve up psychedelic pizzas to the local hippies. When their magic mushroom harvest is contaminated by the nearby chemical plant, their peace-loving customers transform into violent, flesh-eating zombies. Compelled by an uncharacteristic sense of responsibility, Scotty and Dong are determined to fix the mess they unwittingly caused. Along the way, the pair encounter a reclusive war vet, a foul-mouthed granny, a deviant sheriff, and many more bizarre characters.