Written by John Lucarotti, this script came about after "Space Station" was rejected and Lucarotti was suggested by Terrance Dicks as a replacement writer on the strength of his "Moonbase 3" script. The story would use the same space station setting as "Space Station", the setting being dictated by the production office as means of saving money by having it share sets with "Revenge of the Cybermen". Commissioned in June 1974, Lucarotti devised the concept of the ark, a space station that housed a huge plot of countryside the size of Kent – a sort of Home Counties in space. His six-part story concerned the invasion of the ark by a species called the Delc, a spore-like fungus with separate heads and bodies. The final episode was to have the Doctor defeating the Delc leader by hitting it out into space with a golf club, and indeed Lucarotti planned to give each episode a frivolous title, citing "Puffball" as the title of an early episode and "Golfball" as the title of the final episode. When the draft scripts arrived from his home in Corsica, Holmes and Hinchcliffe felt they were far too ambitious and complicated to realise on the programme's budget and Lucarotti had over-conceptualised the story, which meant that it was inappropriate for the viewers. It was replaced by a different story with the same title by Robert Holmes, which shared only the setting with the previous version.