Cockerill was charged with watching for meteorites hitting the surface. On one occasion, he spotted Norna, Tegan and Turlough trying to steal an acid jar. As he turned to stop them, the jar struck his head, dazing him.
When it became known that Plantagenet had been "eaten by the ground", Cockerill decided to join the deserters. The other deserters attacked him and he fell and began to be pulled through the ground.
However, the pull slackened and Cockerill freed himself. Taking this to be a sign of power, the deserters took him as their leader. Together, they took Norna as a prisoner and tied her up.
Cockerill tried to convince the colony loyalists to join him but Norna's revelation that Plantagenet was alive convinced them otherwise. Cockerill and the deserters decided to find out for themselves by going into the caverns. Cockerill and the deserters rejoined the colony after Plantagenet was rescued. (TV: Frontios)