Scientist J P Kettlewell, known for his work on alternative energy sources, created experimental prototype robot K-1 for a group known as Think Tank. Its eventual purpose was to replace human beings in a variety of dangerous and difficult tasks, such as mining operations and operations involving radioactive materials. Over seven feet tall and weighing a quarter of a ton, the K-1 Robot could speak, had the capacity to learn, was voice-controlled, very clever and very strong. The robot was Kettlewell's last project for the Think Tank; when he left the group, he ordered that the robot be dismantled.
Think Tank, however, had other ideas. Members of the group had founded the Scientific Reform Society, a group that wanted to reform the world on rational and scientific lines, ruled by a self-appointed élite. The Doctor surmised that SRS had in mind a rule by the superior types, while the inferior types were guided, helped, and kept away from harmful ideas and influences by wearing and even thinking what the SRS wanted. The SRS was, however, a front for Think Tank's true purposes.
The robot's prime directive was to serve humanity and never harm it; Think Tank learned that they could reprogram and reset the robot's inhibitors, not realizing that this would create a conflict, causing an imbalance in the robot's neural circuits. If forced to go against its prime directive, the robot's mind would be destroyed, making it go mad. And, indeed, when the robot was reprogrammed, it became unbalanced. Think Tank used it to assemble parts for a disintegrator gun which could burn through walls and metal - first stealing the plans, then the control circuitry, and finally the focusing generator - in order to obtain nuclear launch codes that could set off every atomic weapon in the world. They told the robot that the people it was killing were "enemies of humanity" and used it to destroy anyone who tried to get in their way. The robot used visual scanning to receive and confirm its target, which was shown to it by means of a photograph.
The robot took over a bunker from which Think Tank could use the nuclear launch codes. Sarah and Harry, who were taken prisoner, escaped and convinced Kettlewell to stop the countdown and open the doors to let UNIT in. The robot killed Kettlewell and then went into tremendous emotional shock. Not knowing that Kettlewell had changed his mind, the robot decided that Kettlewell's plan had to continue. It would release the nuclear weapons, and when humanity was destroyed, it would build more machines like itself - unlike humans, machines do not lie. It took Sarah, the first person to show it compassion and concern, with it out of the bunker, where the Brigadier fired on it with the disintegrator gun. Unfortunately for the Brigadier, the robot was made of a kind of "living metal" with the capacity to grow like a living organism, and instead of destroying it, the infusion of energy caused it to grow to enormous size. It then kidnapped Sarah and rampaged through the town, crushing people beneath its feet. The Doctor whipped up the metallic equivalent of a virus that would break metal down into an easily recyclable form, and threw it onto the giant robot. A red patch began to enlarge on the robot, causing its growth mechanism to go into reverse. The robot's corroded body eventually dissolved away into nothing.
