Terrified of sheep and dosed up on therapy, Henry Oldfield returns to his family's farm to sell out to his older brother Angus, unaware that something baaaad is going on: Angus's reckless genetic engineering programme.

When a pair of inept environmental activists release a mutant lamb from Angus's laboratory onto the farm, thousands of sheep are turned into bloodthirsty predators. Along with farmhand Tucker and greenie girl Experience, Henry finds himself stranded deep on the farm as his worst nightmare comes to life.