The character of Jane (blonde in solarium) was played by former Miss World Eva Reuber-Staier (who went on to play the recurring role of Rublevich, General Gogol's secretary, in the James Bond movie series), who also played the girl on the monitor giving Zoref his wake-up call.
The first of three episodes where no one leaves the base. The others are The Troubled Spirit (1976) and The Lambda Factor (1976).
In the explosion scene, shots of personnel being tossed around from Breakaway (1975) were included (where a sequence in Reconnaissance is seen, which had been deleted from "Breakaway").
The charred remains of the zombie-like Zoref caused censorship problems in some of the foreign countries when this episode originally aired.
Originally titled "Force of Evil". Filmed May 28th to July 5th, 1974. The whole production was shut down for three weeks in June for a summer vacation (Martin Landau turning 46, Barry Morse turning 56, and Nick Tate turning 32 during the shutdown), a luxury that they couldn't afford while filming season two due to its tight schedule.