 After "Shadow of Fear", the regular characters of Captain Grey and Doctor Fawn, who were voiced by Maxwell and Tingwell, continue to appear in the series but do not speak.Both Tingwell and Maxwell can be heard voicing background characters in the flashback to "Big Ben Strikes Again" in the series finale, "The Inquisition" (Tingwell's voice is also featured in flashbacks to the first episode in "Dangerous Rendezvous" and "Traitor").This episode's incidental music was performed by an ensemble of 15 instrumentalists and recorded during a four-hour studio session held on 22 July 1967.