This episode was filmed simultaneously with Dorzak (1977) (2 to 18 November 1976), which is why Nick Tate isn't involved and the other major actors other than Martin Landau only appear in flashback. None are shown in the Command Center, as one would expect.
The console the Interrogator used to read an unconscious Koenig's thoughts was previously used as the alien monitor/transmitter on The Mark of Archanon (1976).
The mind-reading apparatus used on the heads of Commander Koenig and the Interrogator are actually welding helmets with the faceplates removed.
There's a deleted scene in the final act immediately after Fraser turns his Eagle around when detecting Koenig's signal, where Elizia's subordinates begin to turn on her (leading up to "You doubt me and believe an alien?").