The Guard Captain was the head of the citadel guard on Peladon. He was sent by Ortron to investigate reports of the Third Doctor and Sarah's in the tunnels. He tracked the pair down in the temple and took them to Ortron and Queen Thalira, where Alpha Centauri confirmed the Doctor's identity.
The Captain reported that a group of miners had made a failed attack on the Federation armoury. The Doctor and Eckersley arrived with a captive Preba, prompting Ortron to order the Captain to have both Preba and Gebek, who had taken no part in the attack, executed. The Doctor helped the pair escape, knocking the Guard Captain down to stop him pursuing him. Although Thalira accepted the Doctor's actions, Ortron sent the Guard Captain to kill Gebek and anyone with him. The Captain sent guards after a fleeing Preba and captured Gebek but was knocked unconscious by the Doctor.
The Guard Captain caught Sarah after she was used as a hostage by Ettis in a second, successful raid on the armoury. He took her to the temple on Ortron's orders, then informed Centauri and Eckersley where she was. He arrested the Doctor again when he disregarded Ortron's order not to leave the citadel and stood guard at his cell. He avoided the Doctor's attempt to get the key off him but the Doctor later distracted him with a magic trick, allowing Gebek to knock him out.
He accompanied Ortron when he explained the plan for the miners to return to work in order to convince Federation troops everything was running smoothly. He was later accosted by Ettis and his men when they invade the citadel and told them Gebek was in the throne room. Ettis ordered two miners to take him away as a prisoner. (TV: The Monster of Peladon)