Gyro

The Gyros were spherical robots which served a near-Human civilisation. When a terrible illness struck, killing thousands, the few survivors fled the cities to avoid it. Years later, their children (who now carried a non-fatal form of the disease) tried to return, but the Gyros, which continued to maintain the cities and farms in their absence, would not let them enter, and they had to raid the robots' farms and orchards for food. When the Doctor, John and Gillian arrived on the planet, the Gyros captured Gillian, and one of the natives joined the Doctor and John on a journey into the city. They discovered a second group of survivors, who had sealed themselves inside a building when the sickness struck, and were given food and taken care of by the Gyros, which also kept out the other survivors and destroyed any carriers they found by throwing them into a valley of flames. The Doctor rescued Gillian from this fate, and gave the people the cure for the sickness. (TVC: The Gyros Injustice)