Macroseed, a cutting edge biotechnology company, chooses the small farming town of Hobson to test and develop TX-40. This is a new genetically-engineered strain of fast-growing corn that could increase yields and make the company millions of dollars. Linda Andrews, the veterinarian in Hobson, begins to wonder about the safety of TX-40 when a farmer brings in a dead cat from his field. The cat has horrible mutations, including a giant tumor which sprouts a fifth leg.
Her skepticism grows deeper when terrible, inexplicable tumors begin to appear in people: Mr. Rivers, young Matt Hooper and Eddie, her mentally-disabled nephew. Linda's worry persists while her husband, Rex Andrews and her lover, Harold Zimmer, both of whom work at Macroseed, try to convince her that TX-40 is safe, warning her that her investigation might generate negative publicity that could destroy the town's new-found prosperity.
With some inside help, she gets the test data from Macroseed and, with Doc Wells, begins searching for connections between the new corn and the mutations.
Harold reassures Linda that TX-40 cannot have spread to humans, but she finds out that it has spread from the corn to milkweed plants, and then from the milkweed plants to people who had an increased amount of growth hormone: Old Man Rivers was taking hormone supplements, and the teen Hooper was in the middle of a growth spurt. Linda and the local doctor, Doctor Cooper, confront Harold with the truth. He reveals that he knows, but the company will continue to produce the corn. He shoots Doc Cooper and is about to kill Linda when her husband, Rex, knocks Harold out. The episode ends with a shot of Rex and Linda holding each other while workers in haz-mat suits use flamethrowers to burn the corn and milkweed plants.