Vrall The Vrall were a race of ruthless monsters who were almost unleashed on Earth in the nineteenth century . Biology . As a race , the Vrall were utterly ruthless , highly effective at disguise , and nearly unstoppable . They appeared to be just a very dangerous alien animal used for sport on an abandoned hunting ground on the Moon , but were actually sentient and incredibly cruel . They were shaped like men , but were about half the height of humans and could bend and flex themselves to only a hand ' s thickness . They could change colour to blend into their surroundings . They could also link together to form an even more powerful entity , they didn ' t bleed , and any small cuts or punctures quickly healed over ; one Vrall quickly recovered after being shot three times in the head with a Victorian revolver at point - blank range . The only way to stop one without advanced weaponry was to either dismember one ( difficult since they moved so fast ) or set off an all - consuming fire ( also difficult , given the need to blow up something pretty big to stop them running out of it ) . ( PROSE : " Imperial Moon " ) History . The park in which the Vrall lived had been used as a hunting ground for an apparently long - gone empire , populated by deadly beasts and controlled by something called the warden . The atmosphere was controlled by a force field around a large crater , keeping air in but letting solid objects leave . The Vrall used a species called the Phiadoran s , exiled to the Moon , as hosts . They soon became hosts to the Vrall and remained that way for some time until the year 1878 . Around that time , the Vrall took one desperate chance to escape ; they had seen Earth when the Moon was just right , but knew that humanity would take too long to develop space travel by themselves to be of any use . They created miniature RNA spores encoded with the construction information for a space engine , which they fired out of the dome around the park with a vacuum gun . Eventually , one spore struck the mind of a Professor Boyes - Dennison , who developed the engine with the aid of his twenty - two - year - old daughter Emily . The engines were used on three ships — the " Cygnus " , the " Draco " , and the " Lynx " , which were commanded by Captains Richard Haliwell , Sinclair and Green , with Haliwell in overall charge . After arriving on the Moon ( more specifically , in the park where the Vrall were ) , the original expedition lost one of their men , Sub - Lieutenant Granby , and encountered the Fifth Doctor and Turlough . Posing as a scientist and his assistant , the Doctor and Turlough helped the expedition find Granby . He had , quite literally , had his brains sucked out by the Vrall , who had attacked him in order to absorb his knowledge and learn the Earth language . While trying to get to the main citadel with the Doctor and Turlough , the British party encountered one Vrall in Phiadoran form , apparently in danger . Turlough saved her . She claimed that she took knowledge of his language from his mind to explain her having previously spoken in some kind of odd wailing noise , really just her adapting to English . Calling herself Lytalia , she took the team to the home of the Phiadorans , where they decided to help the British team stop the Warden . The warden had a large force field around its citadel that prevented creatures with a certain DNA pattern entering . Since human DNA hadn ' t been entered into the force field , they could get at the warden . With one Phiadoran per member of the team , they got to the warden ' s base . The Doctor reprogrammed two of the warden ' s flying sentries so he and Turlough could pilot them , allowing them to penetrate the Citadel , rescue Haliwell and Emily , and convince the Warden to deactivate the defences . As the citadel began to collapse , the British soldiers raced back to their ships , as the force field that kept the air in the crater began shutting down with the warden ' s death . The Doctor , Turlough , and Lytalia became separated from the rest , and barely managed to find their way to the crashed " Draco " , only to discover that the helmsman , Henry Stanton , had mutinied and only a few crewmen were left . The Doctor got the ship up , but was kicked out by Stanton ' s crew , leaving Turlough alone on the ship , with the Vrall / Lytalia picking them all off . Kamelion found the Doctor before he could suffocate , and they were able to rescue Turlough before Stanton drained the air out of the " Draco " to stop the Vrall . During his time recuperating in the TARDIS , the Doctor worked out the truth about the Vrall as his subconscious was able to focus on the anomalies that he had only briefly registered at the time , such as their use of the term " mechanical servant " to describe the Warden ' s robots ; " mechanical servant " was a term that would have been used by Sub - Lieutenant Granby rather than Turlough , resulting in him realising that the Phiadorians / Vrall had absorbed knowledge of English from Granby ' s mind rather than a telepathic download from Turlough . Although they weren ' t in time to stop the " Cygnus " and the " Lynx " taking the Vrall to Earth , the Doctor and Turlough were able to return to the park and find some weapons in the citadel ' s armoury that could hurt the Vrall , and destroyed them all in the ensuing battle , with all records of the expedition being destroyed in the aftermath . ( PROSE : " Imperial Moon " )