Codal was a member of the Thal task force sent to Spiridon to defeat the Daleks based there. Codal was the team's scientific specialist. His investigation concentrated on the Dalek's ability to become invisible. He was captured by the Daleks, and spent time in a prisoner holding cell with the Third Doctor. There, the two had a long discussion about the nature of bravery. Codal felt that he was bereft of that quality, but the Doctor seemed to convince him that he in fact was possessed of great courage.