The Catalyst was the fourth and final story of the second series of The Companion Chronicles, produced by Big Finish Productions. It was written by Nigel Fairs, narrated by Louise Jameson and featured the Fourth Doctor and Leela.
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- The Tro'faroom, which was built by the ancient founders of the Sevateem on their planet, is a corruption of "Trophy Room."
- Lord Douglas has encouraged his daughter Jessica to read the works of Thomas Hardy. However, she prefers that of Rudyard Kipling.
- Lady Douglas considers the suffragettes to be "an abomination of nature."
- H'mbrackle claims that he and the Doctor shared dinner in the Royal Place of Kremnon shortly before the destruction of the Z'nai civilisation.
- Leela was named after the Sevateem's first and greatest warrior.
- This story strongly implies that Leela survived the Last Great Time War.
- This audio drama was recorded on 3 June 2007 at the Moat Studios.
- This audio drama was told from Leela's perspective.
- This story is set between The Talons of Weng-Chiang and Horror of Fang Rock.
- This story was originally released on CD and download.
- Leela refers to the destruction of Gallifrey in the Last Great Time War. (TV: The End of the World) As such, it is one of the first Big Finish audio dramas to make direct reference to an event in the revival TV series.
- Leela mentions being cast out from the Sevateem for blaspheming against Xoanon. (TV: The Face of Evil)
- Leela recalls growing up with Tomas and Jabel and arguing numerous times with her father Sole during her childhood. (TV: The Face of Evil)
- The Doctor once again observes, "Where there's life, there's hope." (TV: Planet of the Spiders)
- Leela claims that she was named after the greatest warrior in Sevateem history. However, she previously told Boudica that her name had no meaning. (AUDIO: The Wrath of the Iceni)
- The Doctor mentions he once saw a whole world burning. (AUDIO: The Time Vampire)
- Leela would love to have stabbed Lady Douglas with a Janis thorn if not for the Doctor's forbidden of her doing so. (TV: The Face of Evil, The Talons of Weng-Chiang)