The actors found this story absurd; director Ray Austin (who was also not a fan of this script) had to yell at Catherine Schell because she couldn't keep a straight face during filming. "Be professional!", ordered Austin. In an interview, Schell explained that she wanted to respond to that with "I am a professional, which is why I'm laughing at this badly written script". This had been Austin's second Season Two episode and disliked the script so much (and maybe more than just the script) that after this episode was completed, he'd left a rock on Fred Freiberger's desk with a note on it saying, "I name this rock Freiberger". Everyone took it as a joke, but Austin subsequently quit the series.
The regular cast hated this episode's script (Martin Landau was close to quitting). Fred Freiberger adamantly defended it, insisting that it was the best example of science fiction for Season Two so far (reportedly, Leonard Nimoy experienced a similar incident dealing with Freiberger during Star Trek (1966)'s third season with And the Children Shall Lead (1968), an episode voted among that series' worst). Landau realized that if he had walked away, it would have affected the production on which too many people's livelihoods depended. So, Landau now shared a similar outlook as Gerry Anderson - who only agreed to be involved with the American-run Season Two to collect the paycheck - just trudging on with little enthusiasm (which was why Anderson never bothered to interfere with the sometimes-off-the-wall actions of Freiberger).
This is the only episode that takes place entirely away from Alpha.
Filmed 18 through 31 March 1976. The original script had the episode take place on an asteroid which inexplicably housed an Earth-like atmosphere and gravity pull.
In the scenes with Tony and then Reilly carrying a glowing rock while walking, a wire ran up the actors' pant legs into the papier-mâché rocks. At one point, Tony Anholt dropped his rock and broke it, holding up production.