We begin in a lab. There are four vats, one with a picture of a gorilla, one with a picture of an alligator, one with a picture of a wolf, and one with a warning label on it. Three teenagers, two boys and a girl, are strapped to chairs, and a bearded man in a labcoat walks in, and tells the teens that they're contributing to an experiment that may end cancer once and for all, and he takes six needles, puts three in the vat with the warning label and extracts some of it in each needle, one needle in the vat with the gorilla picture, one needle in the vat with the alligator picture, and one needle in the vat with the wolf picture. Afterward, he injects the substance from the vat with the warning label, a mixture of chemicals, into each teenager, then injects the substance from the vat with the gorilla picture, gorilla DNA, into one of the boys, the substance from the vat with the alligator picture, alligator DNA, into the girl, and the substance from the vat with the wolf picture, wolf DNA, into the other boy. The teenagers then begin trembling as fur begins appearing on the boys and scales appear on the girl. They then begin growing bigger, as do their muscles, and the teens eventually reach 20-feet in height. They are now monsters, a mutant gorilla, a mutant alligator, and a mutant wolf, respectively, and they break out of the lab and head in the direction of the state of Arizona.
Meanwhile, in a town known as "Aberdale", three boys, a chubby pink boy, a thin square-headed boy, and a bald thin boy, are walking together, and arrive at a place called "Millie's Scrapyard". Just as they arrive, however, a car comes crashing down infront of them, and a crowd of people comes running past the boys, who then turn around to see the monsters, who are wreaking havoc on the town. The boys then hide in the scrapyard as the monsters come by. Once they pass, the boys sneak out of the scrapyard, barely escaping the scrapyard's dog. The boys then head to a place known as "Aberdale Elementary", which is in ruins. They then find a woman in torn clothing and broken glasses, who tells them "It's over, they're on a rampage" as she dies from her injuries. The boys then leave the scene after paying their respects. They then find a police squadron, lead by an officer by the name of "Officer Moody", in battle with the monsters, who have the clear advantage. Moody then orders a retreat as she is devoured by the alligator monster. The officers then retreat as the monsters continue wreaking havoc on the town.
The boys then realize that the only way to survive the monsters is to hide underground, so they head to a well just outside the town, and they jump into the well. After at least 20 minutes, the boys wonder if the monsters are gone, and climb out of the well. They then head back into town, and find that the monsters are still there, but much of the town is destroyed, and the monsters head into the part of the town that isn't destroyed and begin wreaking havoc on it as the boys flee the scene, walk up to a hill, and survey the chaos caused by the monsters. Much of the town is in ruins, there are hardly any civilians left. Those that are there are either crushed, burned, trapped under rubble, mangled, running, limping, trying to help their friends or family, crawling, or struggling to get out of rubble. Once the monsters have finished destroying the town, they spot a larger part of the town, head to it, then repeat what they did to the part of the town that's destroyed. The square-headed boy begins panicking, wondering if the monsters will come for him and the other two boys next, and the chubby boy reassures him, saying that even though their home is destroyed, the boys still have eachother, and they huddle in silence as the sun begins setting over the horizon, and the boys wonder if this will be the last time they'll ever see the sun again.