Young Henry Oldfield lives on a sheep farm in
New Zealand with his older brother Angus and his father Oliver. Angus envies Henry's natural gift of farming and Oliver's pride. One day, Angus plays a cruel prank on Henry, terrifying him by killing, mutilating, and donning the carcass of Henry's pet sheep, Dudley. Moments afterwards, Mrs. Mac, the farm's
housekeeper, informs them of their father's death. The combined shock of these two incidents leads Henry to develop a crippling
phobia of sheep. Fifteen years later, Henry returns to New Zealand to sell his share of the farm to Angus, ignorant of his experiments.
Environmental activists Experience and Grant infiltrate Angus' lab and accidentally release a deformed mutant lamb which bites Grant. The lamb then escapes into the fields and bites another sheep. Henry and his childhood friend Tucker visit the farm and notice a sheep that refuses to run away. They team up with Experience and investigate a farmhouse, where they find a farmer's mutilated body. Henry sees a sheep in the hallway and, due to his phobia, quickly hides in a room with the others. The sheep crashes through the door and Tucker shoots it. Henry, Tucker, and Experience drive away, but another sheep hiding in the car bites Tucker. On the other end of the farm, Angus meets Grant, who bites him and runs off. After the car is destroyed, Henry, Tucker, and Experience seek refuge in the laboratory, where Henry learns of Angus'
genetic experiments with his assistant Dr. Astrid Rush, whereby the sheep have turned from docile vegetarians into ferocious carnivores, whose bite can infect and transform a humans and other sheep. When Dr. Rush sees that Tucker's foot has now become a sheep's foot, she keeps him for study. Henry and Experience escape when Angus cannot bring himself to shoot his own brother. Flocks of sheep come running down the hill toward an
offal pit surrounded by a gate. When Henry and Experience accidentally slip into the pit, Angus abandons them, but they are able to escape through caves underneath the farm. They find the original barn that Henry remembers from his childhood. In the barn where Henry was traumatized as a child, they find Grant, now metamorphasized into a monstrous human-sheep hybrid. Back in the lab, Tucker is also in the middle of metamorphasizing, but Dr. Rush administers him an injection of
amniotic fluid from one of the mutant lambs, which undoes the transformation. When Dr. Rush goes outside to give the news to Angus, she is killed by a sheep. Angus gives a presentation about his new genetically engineered sheep to a group of international businesspersons, but they are soon slaughtered by the carnivorous flock, while Henry and Experience look on in horror. Angus finds the sheep are not aggressive to him due to his infection, while Henry and Experience manage to escape with Mrs. Mac, who drives them to the farmhouse. Henry finds Angus, learning he has a
love for sheep and leaves in disgust. Henry realizes he has been infected and, unwilling to risk hurting Experience if he fully transforms, kisses her goodbye. While Experience and Mrs. Mac make their escape, Henry follows Angus to the farm's plane. Angus has now transformed into a gargantuan mutant half-human, half-sheep creature. Henry struggles to fight him, but, governed by a sheep's instincts, Angus is kept in check by Henry and the farm's
sheep dog. While Angus is cornered by the dog, the revolving propeller of the family's plane cuts into him and wounds him badly. Tucker arrive in time to disinfect both Angus and Henry with more amniotic fluid, administered via a medicine nozzle designed for sheep. Tucker, Henry, and Experience herd the mutant sheep into the barn, and Angus enters the barn, hoping the flock will bite him again, but the flock, driven by his bloody wounds, devours him instead. The trio destroy the flock in a methane-powered explosion. The cure is given to the surviving half-human, half-sheep hybrids, including Grant, who are all turned back into humans. While observing the once-again humans, the sheep dog, ominously, bleats like a sheep. ==Cast==