Cybermen on the Moon, as the perennial favourites make their second appearance in essentially a retread of their first. It's 2070 AD and Earth's weather is controlled from a station on the Moon by means of the Graviton. The crew of the station are coming down with a disease that turns out to be a Cyberman-engineered poison. Polly and Ben realise that as Cybermen are part-plastic, solvents ought to harm them, and mix up a cocktail of chemicals which they use in fire extinguishers to defeat the Cybermen on the base.