The species used enormous, half-mile wide, discoid-shaped spacecraft and could create different environments inside. They also possessed mind conditioning technology and weapons capable of destroying worlds.
Alien ambassadors visited Earth some time after making contact with a Human exploration mission on Mars, where one astronaut was accidentally killed. Carrington, the surviving astronaut from that mission, by then a high-ranking British army officer, kidnapped the ambassadors. After forcing them to carry out a series of raids and assassinations his organisation planned to expose their existence to the world, thus stirring up public opinion and forcing world governments to launch a nuclear strike against their spacecraft. This plan was defeated by the Doctor and the ambassadors were returned.