"Space-Whale" was originally pitched by Pat Mills and his writing partner John Wagner in 1980 as a Fourth Doctor adventure. When the production office showed some signs of interest, Wagner left the project and the script was commissioned as a four-part Fifth Doctor story for a scene breakdown on 7 September 1981 and full scripts on 2 December 1981. The new drafts reduced the humor and the renamed "Song of the Space Whale" was now planned as the third serial in Season 20 and intended to introduce new companion Vislor Turlough. The story concerned a group of people living in the belly of a giant whale in space. The Doctor would find this out while attempting to protect the creature from being slaughtered by a rusting factory ship. The castaways living in the whale, as well as the ship's captain, would be working class characters, with the former's dialogue being based on that of a working-class Northern Irish family that Mills knew. During the writing, Mills and script editor Eric Saward "fundamentally disagreed" on the character of the captain (Saward wanting a more "Star Trek"-type figure) and the dialogue for the castaways. Mills has said that "there was a "Coronation Street" quality to it that Eric felt didn't work in space. He thought the future would be classless, and I didn't." Mills' disagreements with Saward led to the script being delayed until it was too late to serve as Turlough's introductory story. The script was then considered for Season 21 and later still Season 22. By this point the script had been revised as two 45-minute episodes, but although it was still listed in July 1985 as an ongoing script, by November 1985 Nathan-Turner confirmed at a convention that the script had been dropped. The "Space Whale" concept was eventually revised and realised in the 2010 episode "The Beast Below". The rejected script was later adapted as "The Song of Megaptera" by Mills for Big Finish's "The Lost Stories" in May 2010.