The secret radio transmitter disguised as a clothes brush, used by Kellman, is the very same prop that appears in Live and Let Die (1973). The prop was handed over by Roger Moore himself when he visited the BBC in 1973. He later told the Radio Times that the props master, not recognising Moore, had paid him two shillings and sixpence for the item: "I'd popped into the Beeb [BBC] for a cup of tea and spotted a notice about an upcoming "Doctor Who", so I thought the darlings would be so cash-strapped they'd need anything they could get their hands on. It wasn't MGM, after all. But I didn't expect to walk out with two and six!"
This serial marks the first appearance of the Cybermen on the series for seven years, since The Invasion: Episode Eight (1968), and their final appearance for another seven years, until Earthshock: Part One (1982). It is therefore their only appearance during either the 1970s or the Tom Baker era.
The decision to use the same studio sets as The Ark in Space: Part One (1975) was made to save the cost of building another set.
The working title for this story was Return of the Cybermen.