Therefore, its known narrative elements are not a part of the Doctor Who universe. It may have been the basis for a similar story in another medium, however — and that story may indeed be a part of the DWU.
Killers of the Dark, also known in fan circles as The Killer Cats of Geng Singh, was an unproduced six-part serial written by David Weir that was to have concluded Season 15. Graham Williams decided another Gallifrey story needed to be written after the success of The Deadly Assassin and commissioned Weir with the task. It would feature Cat-People native to Gallifrey who would live in a culture similar to that of many Asian countries. It would also feature a scene set in a gladiatorial arena, filled with Cat-People. When run past script editor Anthony Read and director Gerald Blake, it was cancelled as they believed it would be too hard to film. Williams and Read then wrote The Invasion of Time to replace it.
The name Killer Cats of Geng Singh is based on a misunderstanding of something Graham Williams once said at a convention. Trying to remember the name of the unproduced story, he said it was "The Killer Cats of... something", and substituted "Ginseng" for the noun he couldn't remember, riffing on the sometimes odd-sounding proper nouns used in Doctor Who. This was misreported in the fan press as The Killer Cats of Geng Singh; this was never the actual title of the story. (INFO: The Invasion of Time)
- The "Killer Cats" of this unmade story are stated to be part of early Gallifreyan history in Daniel O'Mahony's A Rag and a Bone, published in the fanzine Myth Makers Presents: Essentials in 2003.
- The Cat-People of Gin-Seng have since been referenced in PROSE: Invasion of the Cat-People, AUDIO: The Last Fairy Tale, and AUDIO: Erasure; Erasure even mentions them as having once attempted to invade Gallifrey.