Actor Shane Rimmer had a prior association with Century 21, having voiced the character Scott Tracy in "Thunderbirds" and narrated the series' alternative two-part episode format. Impressed by his work, the Andersons asked him to write an episode of "Captain Scarlet". Rimmer immediately agreed and was soon telephoned by series script editor Tony Barwick, who had an outline for an episode titled "Avalanche" and told Rimmer that a courier would "' the storyline over to you in about an hour. Take today and tomorrow and see how you'd go about filling it in.'" Resigning from his part-time job at a sheet metal factory to focus on this task, Rimmer put together a draft treatment over the next 24 hours; he found the characters and plot elements a "heavy mix to juggle with" but managed to incorporate "one or two workable story developments that avoided stepping on the toes of the series concept or any of the main characters." Rimmer and Barwick revised the draft two days after. After the script for "Avalanche" was completed, Rimmer started work on treatments for the episodes "Expo 2068" and "Inferno" – jobs that, in his words, "more or less took care of '67". He later wrote scripts for "Joe 90", "The Secret Service" and "The Protectors".